Well this is our first season in the 5th wheel in freezing temperatures and it has been fun, but a bit challenging. Already had the 10' poop-cycle, freezing water lines, frozen fridge and all the joys of shoveling :) I've gotten all that fixed thanks to a lot of great posts on here. But here's the most recent one.At night, and all day I guess, I've noticed when I put my hand in between our mattress and the slide out wall there is ice build up, even frozen to the wall. I ignored this for a little while, yesterday I decided to put the pink foam-board in between the wall and mattress. i think that will keep the moisture off the mattress. Today I took the cover of our mattress and noticed a bit of mold on the part of the cover that sits below the mattress. So i then looked at the wood that mattress sits on and it is very noticeably wet and moldy. Now it's not from a water leak as it is really only in the middle of the wood frame and not the sides. My guess is that since the slide out bottom is not insulated that the super cold air is condensating to the inside wooden bed frame?? I don't know. Anyone else have problems like this. I'm afraid I'll have to replace the wood, but I just want to try and make sure it doesn't keep doing this?

Your everyday RV is not insulated well enough to use in the winter....some are better than others.

You'll need to raise the mattress so it gets some ventilation on the cold surface. Keep the mattress away from the wall or add a thermal break from the wall to the mattress (a piece of 1/4" foam sheet comes to mind). If it was me, I'd make a new mattress platform with 3/4" space between the new platform and the existing platform. In between the 3/4" ledgers that support the new platform, I'd install 1/2" extruded foam board with foil backing. The 1/4" difference will allow for an airspace so that there is ventilation to the original platform, averting rot, hopefully.

When you shower open a vent or window to draw moisture out get a fan moving air will keep it dry

Sounds like you need to keep the heat on.

Another of the miultitude of reasons my rig does not have any slide-outs.

Cold weather condensation in tough spot... | Good Sam Community

19 Replies

brholt
Explorer II
Dec 25, 2013
82tpsmith wrote:
Well this is our first season in the 5th wheel in freezing temperatures and it has been fun, but a bit challenging. Already had the 10' poop-cycle, freezing water lines, frozen fridge and all the joys of shoveling :)

I've gotten all that fixed thanks to a lot of great posts on here. But here's the most recent one.

At night, and all day I guess, I've noticed when I put my hand in between our mattress and the slide out wall there is ice build up, even frozen to the wall. I ignored this for a little while, yesterday I decided to put the pink foam-board in between the wall and mattress. i think that will keep the moisture off the mattress. Today I took the cover of our mattress and noticed a bit of mold on the part of the cover that sits below the mattress. So i then looked at the wood that mattress sits on and it is very noticeably wet and moldy. Now it's not from a water leak as it is really only in the middle of the wood frame and not the sides. My guess is that since the slide out bottom is not insulated that the super cold air is condensating to the inside wooden bed frame?? I don't know. Anyone else have problems like this. I'm afraid I'll have to replace the wood, but I just want to try and make sure it doesn't keep doing this?

Some options for venting under the bed:

Dri-dek

Hypervent

Drymesh
pianotuna
Nomad III
Dec 25, 2013
Hi downhome,

A moisture barrier on the outside will trap any condensation on the inside of the RV. Best practise is moisture barrier on the (heated) inside, then insulation.
down_home
Explorer II
Dec 25, 2013
The cure is going to require insulating with a moisture barrier on the outside.
Look at the clearances you have on the bottom, of slides and sides and top.
If it is feasable since I bet the exterior box is aluminum apply insulated board or material on the inside, in contact with the aluminum. It means it can't adsorb moisture and will have to cover to the edges. Then some provision for air to circulate. Like others have said it may require little fans. I'm basing this on what I've noticed about ours except the slide is insulated.
pianotuna
Nomad III
Dec 25, 2013
Hi Deb,

That, unfortunately, is treating the symptom instead of the disease. In my experience the desiccant devices don't work too well.

The temperature in the area needs to be kept above the dew point.

Deb and Ed M wrote:
I wonder if putting a desiccant under the bed would help?? One of those plastic containers with salts that attract moisture?
Deb_and_Ed_M
Explorer II
Dec 25, 2013
I wonder if putting a desiccant under the bed would help?? One of those plastic containers with salts that attract moisture?
westend
Explorer
Dec 25, 2013
pianotuna wrote:
Hi,

Cut two holes at opposite ends. Put a 12 volt computer fan in one to suck air from the enclosure.

Yup, good one, maybe even two fans, one blowing in and one out.

Mold needs three things to exist--proper temperature, correct humidity, and a compatible surface that offers a food source. Eliminate any one of the three and mold will go away.
Dilute bleach will kill the mold and spores, as will original Lysol cleaner and mouthwash that contains Phenol so you have your choice of residual smell from the mildicide.

Your idea of sealing the plywood with paint is a good one. It will help with any humidity trying to get into the plywood. The key to all of these issues in an RV is ventilation and keeping the humidity low when heating in cold weather. A dehumidifier may prove to be a big help if you're full timing in the Winter.

Good luck with your moisture issues, some of us only wish this was our worst problem.
doxiemom11
Explorer II
Dec 25, 2013
If you are parked in one place, how about putting some insulation board around the outside of the slide - floor,walls,top. We also have a lot of moisture on the window frames and dry the windows and frames, open curtains, open the bed. Also ---- if you have a memory foam mattress you needs to have the ventilation base between the board and the mattress. Condensation from your body will make the board/mattress wet if you don't. We have never had ice or mold, but we do leave our furnace set at 60 at night so we do heat the interior.
Fizz
Explorer
Dec 25, 2013
Double yes on the fan.
You have to get the air moving in there.
JimM68
Explorer
Dec 25, 2013
pianotuna wrote:
Hi,

Cut two holes at opposite ends. Put a 12 volt computer fan in one to suck air from the enclosure.

Agree completely. Open it up under the bed, add a couple small fans.

Also insulate the bottom and maybe the sides of the slide from the outside, use foam boards, seal it as good as you can.

You need to prevent moisture from sitting under the bed and condensing.
Reducing the cold under there will help, and so wil circulating the air.

spray with bleach to kill the mold that is there now, though most will die as it dries out.
pianotuna
Nomad III
Dec 25, 2013
Hi,

Cut two holes at opposite ends. Put a 12 volt computer fan in one to suck air from the enclosure.