We too have a few kids on stretchers, what we have done is cut up an eggshell foam sheet and made ( wife made ) a mini dooner cover to go over the foam, we then put his on the stretcher under their -9 sleeping bag, once they are in them they dont get cold, bit of winging for the first few moments till they warm the sleeping bag a bit.. this seems to stop the cold from underneath and gives them a slightly softer sleeping surface, we just throw them all on our bed with all the sleeping bags when packing up. I like the aircell under our mattress idea, have some left over from when i built my shed will be sticking that under the mattress this weekend.