I’m currently living full time in my RV and have spent many Arizona or Texas nights in sub-freezing nighttime weather without heat. I just pile the blankets on the bed (usually 3-4 will do it) and when I get up I throw on a heavy bathrobe put on some warm slippers and use my propane range top to make coffee and a hot breakfast which warms up my RV pretty quickly. As far as any extra heat, I use a small $20 electric space heater I bought at Lowes. In the future, when I start boon-docking more I’ll pick up a catalytic heater.
I use my RV as a comfortable home base and range far and wide in my 2005 Caravan as well as back-packing. A year ago I enjoyed several fairly cold-weather early May overnight trips up into the high Sierra Nevada’s sleeping in my Caravan. For sleeping in my Caravan, I use the dinette cushions from my RV as a mattress (and also important for under-insulation). A good sleeping bag (not necessarily down) and a stocking hat keeps me nice and warm. This is mainly a guy thing, but using a pee bottle in really cold weather will save you from having to leave the warm confines of your sleeping bag when nature calls. Just one of many things I learned during my past middle-age crazy years when I did quite a bit of mountaineering and tent camping in sub-zero weather.
Steve
BTW fleece blankets are excellent!