RE: Memory Foam Mattress Toppers
I (and several other WetWesties) have been using the memory foam mattress
toppers that Costco was selling a couple of years ago.  These are about 2
1/2 " thick and have a mattress cover that they come in.  Mine is just
single width, cost about $89 IIRC.  These are meant to go on top of a
regular bed at home.  They are just the right length and when simply folded
in half fit behind the rear seat when the seat is up, no need to try to roll
it up.  It does take up room but I find it well worth the effort, I actually
sleep better in my Westy than I do at home.  If shopping around you will
find different thickneses, densities and a wide range in price.  I've never
seen the memory foam in the egg crate design, I've only seen the traditional
foan mattress toppers in that form, like they use in hospitals.