How to Insulate an RV Underbelly

Anyone who has lived and traveled in an RV knows that insulation is its worst enemy. The big hunk of metal and fiberglass does not provide much protection from extreme weather. When it is too cold outside, a motorhome tends to dissipate heat a lot quicker. As a result, the cabin temperature never stays at a comfortable level for too long. You constantly need a heater to give you warmth and that jacks up the energy bill.

So, what do you do? Do you keep wearing a sweater while you are trying to relax inside? Some would say, yes. But that is not a viable solution.

What you need is a permanent solution that helps retain heat inside the RV and the best way to do that is by insulating the RV’s underbelly.

Also, for greater comfort, it is always necessary to have hot water. And you always need to know the answer to a question about how to tell if RV tank heaters are working.

Benefits of an Insulated Underbelly

-Protection against rodents and insects

-Water pipes are protected against freezing, bursting, or leaking

-Water stays warm when reaching the shower head or sink

-No exposure to grime or salt prevents corrosion

-Keeps the RV’s floor warm

-Helps regulate the motorhome’s cabin temperature

Which Material is best for RV Underbelly Insulation?

RV insulation is common in areas that have a colder climate. Sometimes, the RV sold in those places comes factory-fitted with insulation. So, before you even think about investing in insulation, you should check the underbelly for any existing solution.

If there is a coating underneath, you won’t see it without removing the thin coroplast sheet. If you can find some insulation already installed in your RV, you can decide to reinforce it or remove it entirely to install some other material.

There are two materials most commonly used for RV underbelly insulation.

Spray Foam Insulation:  This is the best option if you can afford it since the foam fills any cracks, holes, or gaps with relative ease. It latches onto the pipes, water lines, or other plumbing without you needing to adjust. Moreover, the foam doesn’t loosen up over time, exposing the plumbing underneath the RV. However, if you drive a lot in hot/warm conditions, then spray foam insulation won’t work for you. Therefore, it is only effective in a cold climate.

Foam Panel Insulation: The second option is to install foam padding underneath the RV for insulation and protection. However, you have to be very careful when installing foam panels, because you could easily damage a pipe or a storage tank while attaching them. The panels come with some metal screws and adhesive to fit them in place. But even after sticking them to the underbelly, the panels can loosen over time and fall.

How to Properly Insulate the Underbelly?

Lift the RV from the Ground: The only way to comfortably insulate an RV’s underbelly, you must lift it higher up from the ground using a few strong jacks. But you must ensure that you perform this operation with the utmost care. After all, you don’t want the RV to fall on you while you are busy with the insulation work.

Attach Lights for Clarity: Motorhomes are massive structures and it is really dark underneath them. So, you need to attach a few lights to see everything clearly. This is necessary otherwise you could do some unnecessary damage to the underbelly.  

-Take Pictures on Your Phone: You must also take a picture with your phone, to use later for reference. When you are cutting the panels, you want to make sure their shape and positioning is ideal. Otherwise, you would have to repeat the process and that would waste money and time.

Measure the Underframe: Up until now you were preparing yourself and the RV for the installation process, now you start with the actual procedure. First, you must use a tape measure to note down the dimensions of the underbelly. This includes its size and measurement of its depth.

Remove all the Pipes: Once you have all the measurements and a rough diagram is complete, you can start removing the water and sewerage pipes that are in the way. But remember to shut off all the pipes before disconnecting the joints and connections.

Cut the Foam Insulation: The foam panels must be cut according to the shape of your RV’s underbelly. You want to cover all the nooks and crannies, as well as any exposed areas. Otherwise, the insulation would not work according to plan.

Apply a strong Adhesive: You need to apply a strong adhesive to hold the panels in place. But glue only works as backup to the various screws you have to install in some places.

Rejoin the Pipes and Hoses: The water pipes and sewage hoses you removed from the underbelly must be put back in their correct positions. When you do that, you must ensure that all the joints and connections are secured tightly. If you have PVC material, you need to use the proper sealant for it. Otherwise, leaks could spoil the insulation.

Attach the underbelly cover: Most RVs come with an underbelly cover, so if your RV has one you should put that in place over the insulation and pipes. If you don’t have one, consider buying one as it helps support the insulation material. 

That’s about all you have to do to insulate the RV’s underbelly using foam panels.

Using Foam Insulation

Foam insulation is easy and it requires a lot less time and expertise. All you need to do is raise the motorhome using jacks, attach a few lights for guidance, and buy numerous foam containers for the insulation.

Start from one end and cover the entire underbelly in foam, except for necessary outlets like the ones coming from the septic tanks. Go through the process slowly so as not to miss any areas.

If you follow these simple instructions, you will be done with the job in a few hours!


Underbelly insulation is necessary if you intend to drive and live in a cold area. RVs require extra protection as they are more exposed to the weather elements. Therefore, it is best to invest in insulation now before the winter season arrives and the prices rise.

Leave a Comment

Read more