I also have a two inch memory foam on top of the heated mattress. It works very well. I usually don't like a lot of heat when I sleep, but I put it on when the weather dipped into the low 40's. It was quite efficient turned halfway up. It got too warm. I had to turn it off. Next time I try it in the spring, I'll try it only on the lowest setting.
Audi Q5 + 2015 A-122S = happy camper!
2015 A122S "The next campsite tour of this type of intriguing camper will begin in approximately 15 minutes. We ask that you refrain from any flash photography as it tends to wake the native inhabitants..."
Camped 6 times in 2014, 5 times so for in 2015