I've used a Queen/Double inflatable in my 03. No head room and it curled on the sides, but it was sure comfy. I now use a thermarest backpack pad and backpacking inflatable sleeping pad. Plenty warm enough to leave back open on 30 degree nights and ample comfort. I'm scrounging garage sales for a used 4 person tent I can modify to cover the back hatch.
Find me an RV that can go where my X can!
_________________________
When hell freezes over, I'll ski there too!