my advice is always worth what you pay. read up on thermal bridges if that's any help.Please tell us what in a RTT acts as the "Vapor Barrier"? I don't think this is a good model of the mattress & tent floor situation. There's always some moisture in the air. It condenses on a cold surface. The trick IMHO, is to only let the moisture laden air contact a cold surface where there is air flow, such as the tent walls.
No doubt. But HOW under a mattress do you get AIRFLOW? The mat does not give you airflow, it gives you insulation or it basically gives another 1/4" between mattress and floor of RTT.
I think I agree with this statement more than what you're trying to push: