I love memory foam. Did a king-size DIY-tempurpedic for about $250 from the info on the memory-foam thread on fatwallet.com and it is the absolute best bed I have ever slept on. Previously I'd been sleeping on a $1K+ mattress and it was killing my back, like almost impossible to climb out of bed. With the cheapopedic set up, my back stopped hurting within weeks. Its been at least 3 years now and never a problem.

But I don't think I could comfortably fit in the cargo section of the VX, mattress or not, you must be like 4 feet tall.