I routinely roll from back to side and occasionally wake up with part of me off the pad, but it doesn't seem to bother me 6'0", 180lb.). I've never noticed a problem with ballooning on mine. Different strokes, I guess. My pad is 15 or 20 years old, and doesn't have the higher friction 'patterns' or fabric that many of the new ones have; you bought a can of some sticky substance with the pad and sprayed it on the top to keep you from sliding to the side or, more often in my case when sleeping on a slope, down towards the foot. It used to work, but I think it's pretty much worn off.ehunter wrote: I also have the 1.5 in thermarest. What bugs me about it is when I sleep I tend to roll around from flat on my back to my side. The parts of my body, knees/feet/backside tend to slide off the pad enough to where I notice it and it bothers my sleep. I am not a big guy, 5'8", 145lbs. This is why I bought the prementioned pad 30in-er. However if I had to do this again
I would buy the equivalent 25in-er. I think the 25in may allow me to sleep with one of the back seats still in place, creating an extra place to put stuff.
My 1.5in Thermarest also balloons around depending on how my weight shifts which is also bothersome. But the 4" thick one I have now... NICE! Was the most comfortable I have been on ever. In retrospect though I think the 25in one may present more options in the leaf.

I routinely have gear stored alongside my pad in my Forester as well as on the front seats/front pax floorwell and rear floorwells, and would want to keep all that off the pad as you say. Trying to sleep off to one side with only one seat down wouldn't be an option given how far the shock towers intrude in my car, but I think the LEAF may be wider between them.