Originally Posted by Jgbrown
The ventilation is where the hypervent comes in(or similar product) allowing those air changes to pull the moisture out from under the mattress . However, I think that insulation makes a huge difference too, as in the example of hull temperature, if the insulation keeps the surface temperature 10-15 degrees warmer(and based on my floor vs before insulating the surface, it does) that can certainly help to prevent the condensation forming in the first place.
As a secondary benefit, if it means that the air in the boat stays warmer until it is exhausted from the boat it would mean it holds more moisture.
The hyperdry in lockers at least is less about insulating, it just prevents things from touching the hull and giving that dead air space for mold to form. I've used it in my lazarette and it's making a big difference in how wet things stay(the hatch leaks badly).
I knew about installing "things" under mattress's & cushions just never made that connection to the hull or lockers. It does make sense to use a product that allows air to circulate behind it. An air space in itself is an insulating layer. Not much of one when we look at the R value but many older buildings relied on that air space prior to the development of insulation.
My only concern would be with a solid foam, fiberboard or batt type of product. The potential for moisture to get trapped behind it & create an environment for mold is there in my mind.