Ok, almost a year later and planning another trip. I'm still considering this to be a learning camper, not the final version but thought I'd improve it a bit for this trip. So, I pulled out the giant mattress I had in there and started improving. A local store has closeout deals on various flooring and other home materials, so I picked up a 6' x 8' chunk of linoleum with a simulated wood flooring appearance - went down with zero trimming required.
I then built a wood bed frame that expands from taking a 22" wide cushion to 44" wide. The same closeouts store sells nice, new foam blocks in various sizes, and I got 4 pieces 4" x 22" x 36". It was the best price I could find on foam - $11 each.
Here are some pics:
Frame collapsed (and yes, I am short one slat):

- IMG_1646.JPG (96.4 KiB) Viewed 461 times
Bench Mode:

- IMG_1649.JPG (73.71 KiB) Viewed 461 times
Open 36" wide:

- IMG_1643.JPG (96.1 KiB) Viewed 461 times
The idea is kids can sleep under the bed if needed. The bed is higher than ideal for this reason - to get 16" height underneath it.