i guess it's a matter of personal likes/dislikes.
we have found the 1 1/2" therm-a-rests to be the "answer". we leave them under the TM matress, with the valves at the head facing toward front of trailer. this allows them to be inflated/deflated more conveniently. we had not tho't of placing them differently for hot/cold sleeping. we will check it out. til now, we have had superb comfort in all situations with them under the mattress. on a trip last month, we did use them on top of TM matress--it worked fine if you have a sheet over them--i found the stay-tek covering on the pads is too "sticky" to allow easy turning, unless pads are covered. so--we leave them under mattress.
we tried various foam pads from egg crate to a little more sophisticated types, and went back to the T-a-R.
we travel with them deflated. and when we leave the TM down for storage, we take them out--don't want heat build-up(or sub-freezing temps)
to damage them--they ain't cheap.
we use the performance light series. i have also used the camp rest model--it was glorious, and worked just as a well- a tad thicker at 2", but no prob. sleep well!!
2swans