The air inside a camper warms up quickly but the interior items take a bit of time to reach room temp. My DW found out when she sat on the toilet in our "warm camper" . She screamed so loud I thought she fell in.
I line the headboard and under the bed with reflectix from H. Depot or those cheap foil sunshades for car windows. I bought a bunch at a dollar store and lined my cabover bed, under the bed, along the side rails and headboard area. It worked well until I turned on my LED flashlight and nearly blinded myself reflecting off the foil.
elec. heaters are fine but I always run the furnace as well to make sure its working.
Mattress warmers come in 12 v or 110, I have used both .
Yes, if you run a 110 v. warmer then you need an inverter. It doesn't pay to run a genny. I use a PSW 200 watt inverter that uses a 12 v. plug to op. it . $125.00
The 12 v blankets work fine, I use one to pre heat the bed, so I can pull into a rest area and snooze.
