I did this with an 01 sienna. I got a folding cot, bungeed it to the chair hooks, and got plastic totes the right size to slide under it.
I installed a fantastic vent fan in the roof. The wires came down thru the toolkit compartment and i clamped them to an extra battery under the bed when i was traveling. Having that fan made it so much more comfortable.
For The windows, i cut pieces of reflectix and pressed them in place when needed. The rest of the time i slid them under the mattress.
I hung a curtain on a dowel behind the front seats.
I like it! Simple and straightforward, that cot looks rather comfy too.