Foam prices have skyrocketed in the last year. I'm perfectly happy with the medium foam mattresses I've made for my Caravel
and Overlander, but the mattress for the Sovereign
is going to run a little over $300, just for the foam, which is about 3 times what it would have cost maybe 2 years ago.
The best solution I can find is a 80x60 queen foam mattress at WalMart (about $260). It's 8" thick with 4" of memory foam on top. I'll use a bandsaw to cut the one corner to fit the curve of the shell (rear bedroom).