I'm in the process of improving the cushions/mattresses on two of the bunks in the saloon.

I've decided on 2 layers - a 50mm thick closed cell foam base, topped with a 50mm latex (softer) sheet. Feels comfy to lie on.

Help with choosing a Mattress Underlay:

Foam mattrresses are know to get damp when used on a solid surface like a ply bunk.

I don't really want to do much carpentry on the bunk bases - like building slats etc.

So I've been looking at ventilation underlays. I've seen a few products advertised on the web, like Hypervent, Aero-mesh, Air Cushion. They all look like an "airy carpet".

They are not cheap - one store quoted $100/sq metre for its underlay. Whitworths has Aero-mesh for $100 per 2mx0.9m.

So anyone with feedback using one of these "ventilation" underlays - how well do they work?
If you place them on a seat under a cushion, do they get squashed and go flat ?

Somebody suggested to me that there are alternative products that can be "used" for this purpose, although they are not marketed as such. Think he mentioned a drainage mat of some sort. Any alternative suggestions or solutions to combat under-mattress dampness are welcome.

Ikea bed slats. Check out their web page and find the slats. The Poms use these under their boat mattresses. Cut the slats to suit the width and re install in the holders. Can also be used in the forward bunks that taper down or even full width at the bow.