When we cruised Mexico aboard Camille we had very few issues with moisture and condensation. Baja is a desert and the windows were always open to keep the air flowing. Here in the Pacific Northwest, we have the opposite: rain, cold, and closed windows at night. A cushion resting against the hull will be damp in no time. The diesel heater helps to dry things out at anchor. When we are at the dock, we use space heaters pointed at closed-off spaces.
One of the biggest moisture collectors is the bottom of a mattress after sleeping on it for a night. On Camille we had a (rather expensive) Froli (Amazon) system under our mattress — mainly to try and give our thin mattress a little more bounce. On Limerick, we have a great mattress but nothing to deal with the condensation. So we picked up some Hypervent which came highly recommended by a great online group of women sailors I am part of (if you can’t find it there is a similar product on Amazon and an all-natural alternative). We cut it (quite easily with scissors) to also come up the edges of the mattress where it touches the outside hull.
It is working out fairly well. The bottom of the mattress is staying dry. Now the moisture has moved below the Hypervent but seems to be drying as the day progresses. I had expected no condensation, but I guess that is a bit much to ask in this climate. We’ll be purchasing more Hypervent for the V-berth.
We eventually solved the problem of the moisture under the Hypervent by drilling several 2-inch holes into the wood under the mattress so air could circulate from the storage space below. After that, we had zero moisture buildup.
We absolutely *swear* by HyperVent. We tried one piece of it, then went back and bought enough to put under and behind every single upholstered surface on the boat, and under the book shelves as well.
I’m just doing laundry and in the process checked under the mattress. It is pretty darn wet under the Hypervent. But at least the mattress is dry.