Moisture behind mattress? (Cold caught us)

If you are getting water intrusion and you don't have the cabinets exposed to inside air, you might have a roof or leak along a seal. Check all sealant areas.

We found that we were getting water on the walls of cupboards that were along the outer walls. We now put dehunidifier units (chemical things with a bucket -- I forget the brand name) on the floor of the closets. i started by thinking there was a leak.
We had the mattress/sheets freeze to the back wall.

joelc wrote:
Pull your mattress away from the wall about an inch so you have air flow behind it.

We full time in the PNW, I placed two about 10" pieces of 2X4 vertically at the head it work very well.

Turn the AC on so it runs every once in a while.

"I'm thinking to leave the roof vent cracked open while the furnace heats us overnight so any moisture can leave."

Yes, that's a great first step. Good ventilation along with heat and a small dehumidifier will work wonders for condensation problems.

Good suggestions from everyone above.

It may be well-nigh unavoidable. If the inside of the exterior wall is cooler than the dew point of the air in the RV, you're going to get condensation; so the only options are to reduce the humidity of the air inside (and that may make it a lot drier than you care to be breathing) or raise the temperature of the wall, say by moving the mattress aside for awhile...or going somewhere warmer.

If it were me, I'd probably just move the mattress aside during the day to give the area a chance to warm up and dry up/air out, and not worry too much about it beyond that. Obviously taking reasonable steps to control the inside humidity is also a good idea, such as cracking a roof vent or two. Cooking, breathing, and showering all add a good bit of moisture to the air, and it's rather inconvenient to live without any of them, to say the least.

If you don't mind input from a non-expert, I would say you are on the right track. As joelc pointed out, the mattress insulates the exterior surface allowing it to be cooler, yet it provides no vapor barrier. My concern, since there may be 5 people in the rv, cracking the roof vent may be inadequate. I think a couple inches open on the vent and perhaps a window open as well.

"Pull your mattress away from the wall about an inch so you have air flow behind it." x2 and check the area carefully daily.

Pull your mattress away from the wall about an inch so you have air flow behind it.

Have you tried praying? If that doesnt work i would continue to look towards science for the answer.