Because we boondock most of the time, we rarely get to use our heated mattress. Last year, in the fall, we spent a few nights at a Colorado KOA (i.e. Full hook-ups), and used the heated mattress for the first time. It got pretty chilly at night, but that heated mattress kept us toasty warm. I must say it was one of the most comfortable nights we've spent in our camper.
11' Dodge Ram 3500 DRW 6.7 Cummins
12' Rockwood Roo 233S
3 Akitas (RIP D-Dog)