Hi Folks,
I've been in on this a cupla times, 10/26 & 29 at least, here's an update on us.
We bought 3" egg-crate mem. foam initially (abt $65), and tried it at home on our very firm mattress. Tried it with either side up, liked it with the egg crate side up best. We liked it enough that we thought we'd try 3" "flat" mem foam for home, and use, as originally intended, the egg crate on the boat. We got the 3" Serta "good stuff' (High density 4-lb. solid Visco elastic memory foam) thru overstock.com, about $130 for cal-king sized I think, and are very happy with it at home. We tried it with a quilted mattress pad on top of it, didn't like that, so now have a fitted plain sheet over it as a cover.
We have a queen size bed, the cal-king needed to be trimmed in one dim. only, abt 6", did it with electric carving knife. Note that this foam, and the egg-crate, did shrink an inch or 2 in width & length after use.
Haven't yet cut the egg-crate to size for the V-berth, but will soon, and Pat will make up a plain sheet cover for it.