How to insulate An RV Underbelly To Keep Cold Out & Heat In

Cold weather RV-ing can mean different things to different people. People who camp in the desert, may simply not want to lose heat through the floor at night.

Those who use their RV as a hunting base camp or who go on winter vacations want to preserve warmth or walk barefoot.

For ice fisherman, RV floor insulation can make all the difference between a day of frozen-toe misery, and a nice time living out on the ice.

If you are thinking about insulating your RV’s underbelly, you have several inexpensive options to choose from. External skirting, underlayment insulation sheets, and spray foam are some of the more popular options for insulating an RV’s floor.

In this article, we’ll look at various ways to insulate an RV underbelly, as well as ways to minimize heat loss during cold conditions.

How Do I Safely Jack Up An RV?

This is another time where you need to stick to the mantra of “Safety First.” Before you even set foot in a hardware store’s building materials department, you need to make sure you know how to safely get under your RV.

If you have a fifth-wheel camper with built-in hydraulic leveling jacks, this is relatively easy. If you have a large motorhome, you might be able to shimmy under it.

If it has adjustable ride height suspension, try to set it to the highest level, and see if that gives you enough room to work comfortably.

How To Jack Up A Travel Trailer

If you are working with a travel trailer or popup camper, you shouldn’t just assume that the bottle jack in your car or pickup will be able to handle the job!

A big sheet of old cardboard will go a long way toward keeping the back of your shirt clean.

Get To Know Your RV’s Underbelly

You should spend some time getting to know the details of the undercarriage before deciding on your insulating method. With a small travel trailer, there isn’t necessarily a lot under it. 

In contrast, a fifth-wheel camper or a motorhome typically have a lot going on in the undercarriage.

You don’t want to risk accidentally damaging a brake line, or a tank when installing the insulation of choice.

It’s well worth it to take some extra time to come up with a plan for how you will handle all those various components.

If you are contemplating taking water lines and wires apart for the install, this is a good time to start labeling things.

Snapping pictures with your phone will help, but I wouldn’t recommend using this as your only labeling method.

Chances are you will need both hands during the install and reconnection phase.

A two-inch section of duct tape folded over into a sticky tag, labeled with a sharpie marker will let you see what goes where without having to figure out a way to hold your phone.

Then simply stick a tag on the thing you plan to disconnect, and the place where it attaches. This lets you put A with A and B with B.

How Do I Get Adequate Light Under My RV?

The underside of an RV can be pretty dark, and if you are trying to insulate it during the fall or winter, chances are you won’t have a lot of natural sunlight to work with.

A headlamp is a necessity, but it might not be enough. A headlamp is certainly preferable to holding a small flashlight in your mouth all day.

Handheld lights and flashlights can sometimes get in the way or make a lot of shadows in the nooks and crannies of the RV frame.

If you go into a hardware store’s electrical department you might be able to find some very inexpensive LED rope lights. You can lay them down in the area where you are working to cast a soft light to augment your headlamp.

They usually have a durable protective coating, which allows you to roll over them and drop things on them without breaking them or scattering broken glass is your workspace.

What Are My Insulation Options?

There are a few different ways to insulate an RV underbelly. The type of RV you have, your budget, and how much elbow grease you are willing to put in will all be major factors in determining the one that is right for you.

Rigid sheets of insulation or foam panels are popular, though some people are turning to spray foam insulation. 

Using Foam Panels Or Insulated Sheeting For My RV Underbelly?

This is the least expensive option It’s available in various thickness and R-factors. You should be able to find it in the building materials department of just about any large retail hardware store.

Step One: Measure the total square footage as well as the available depth of the frame.

Determining the thickness and amount you need first requires you to get under your RV, take some careful measurements of the length and width of the underbelly as well as noting the depth of the frame.

This method is much easier with a travel trailer camper or a popup camper than it is with a motorhome. 

Installing the sheets often requires you to disconnect wires and water pipes. It’s not the sort of thing you start early on a Saturday morning and get done in one day.

Step Two: Disconnect Any Necessary Pipes and Wires From The RV Underbelly

In the case of a simple travel trailer, you might be able to work the foam sheets under into place without disconnecting any of the pipes, wires or lines.

A small hand saw will allow you to make any careful, or creative cuts in the foam sheet to help it fit snug.

If you have a fifth-wheel trailer or a motorhome, chances are you will need to label wires and pipes before disconnecting them. 

Of course, you want to make sure that all your tanks are empty, and the power has been turned off first.

With some RV’s you can detach the wiring and pipes to pull the entire underbelly section out.

This is handy for installing the insulation and spares you from having to spend a day laying on a piece of cardboard.

Step Three: Attaching Sheets of Rigid Insulation

Attaching a foam sheet to an RV underbelly takes a little more work than if you were installing it in the basement or attic of your home.

Hardware stores sell special ring shank nails with large plastic washers for attaching foam sheeting in a home. 

This isn’t ideal for an RV underbelly, where the vibration of travel can gradually loosen nails.

Instead, I would recommend replacing the nails with coarse-threaded screws. You should also apply some heavy-duty construction adhesive to the underbelly for added insurance.

It’s especially handy in places where you don’t want to accidentally drive a screw into a tank or wiring loom.

Step Four: Reinstall the Pipes and Wires To the RV’s Underbelly

Once you have the sheets of insulation secured in place you can start the process of installing wires and pipes.

It often helps to have one person under the RV doing the reinstallation, and another one passing components and tools to them. 

Step Five: Insulate Any Exposed Water Lines

Frozen pipes can be a major problem. Even a few hours of temperatures below 32 degrees Fahrenheit can potentially damage a pipe or a fitting. 

With drain lines,, this can be an inconvenience. With pressurized water lines, it can be a major catastrophe that robs you of water for the rest of the trip and will likely cause major damage.

The same pipe insulation that they sell in a hardware store plumbing section will help to prevent water lines from freezing.

It comes split down the middle, allowing you to slip it over the pipe in a continuous sleeve.

Even though it holds firm of its own accord, I would still recommend wrapping it with a zip tie here and there to keep it from moving around.

Usnig Spray FoamTo Insulate My RV’s Underbelly?

Spray foam insulation has become increasingly popular in recent years. Some RV dealers, repair shops, and even home remodeling companies can spray open or closed cell insulationon an RV’s underbelly. The price can vary depending on where you go and the type of foam they offer.

There are times of the year when business is slow for home remodeling and insulation contractors.

With a little bit of dialing and phone conversation, you might be able to find one who is looking to fill their schedule and will spray the underside of your camper for cheap.

Ideally, you want “Closed Cell” spray foam. It is essentially waterproof and will adhere cleanly to the underside of the RV.

If you want to do it yourself, you need to carefully read the label on the spray foam cans sold in hardware stores.

You don’t want to use “Open Cell” spray foam as it can potentially break down as time goes on, letting loose from the underbelly in chunks. It also tends to be a little more inviting for intrepid rodents looking for a home.

How To Use Spray Foam Insulation On An RV’s Underbelly

Spray foam can expand rapidly. If you are installing it yourself and you’ve never worked with it before, give it a few test sprays to get a clear understanding of how much it expands.

When you apply it, you don’t want to accidentally trap things like brake lines and water pipes in it.

Step One: Protect Sensitive Areas

Some simple wood frames can be placed around key components that you don’t want to contact the spray foam.

Set the protective frame in place around any lines or components that you want to protect before you spray.

It’s can be a little bit meticulous, but still faster than removing and reinstalling the pipe or brake line later.

Step Two: Carefully Spray the Foam Into The Desired Areas

It’s best to spray a small amount in a wide swath. Then give it a moment to properly expand.

Step Three: Clean Up Any Overspray Areas

If you do end up accidentally getting some overspray on something you want to leave clear, try to clear it away before it hardens.

Most spray foams firm up in a matter of minutes, then take a day or two to fully cure. If you do have a little bit of overspray, you can use a hand saw or a keyhole hacksaw to carefully cut away the excess material.

Can Exterior Skirting Help Prevent Heat Loss?

As the name implies, this is a rigid skirt of plywood, siding, or sheet metal that you place around the base of the RV once you are parked up.

Some hardware stores even sell decorative panels that look like a home’s foundation.

Skirting is a less permanent option that can help to significantly reduce heat loss through your RV’s floor.

It’s a standard for ice fishing shanties and convertible “Fish House” campers that spend months on frozen lakes in northern states.

Transporting the skirting with you does eat up a lot of storage space. If you are designing it yourself, you might be able to set it up to slide into a convenient space, like an unused overhead bunk, or a rear storage compartment.

Once you place it around the RV, it helps block out wind and the potential hard-freezing effects of windchill.

It’s especially important for travel trailer campers that double as an ice fishing shanty in the winter.

If there is snow surrounding the RV, you could shovel a little at the base of the skirting. This will further block out air leaks and windchill problems.

Just keep in mind that the ambient heat of the RV could melt the snow. When it comes time to pick up and move again, you should plan to give yourself an extra 10 or 20 minutes to carefully chisel out the skirting panels.