Not for road trips but for while parked for the winter. We've had a deLonghi oil-filled radiator for quite a while and used it in the house for supplementary heat in the bedroom. I decided to use it to keep the interior of the MH above freezing (the winters are usually fairly mild here).
The "gadget" I found was a plug-in programmable digital thermostat. It has a 3-pin 15A plug on the back and a socket on the front. Plug it into one of the 115V sockets (or to an extension cord if you want to monitor the temperature other than at the plug), plug your heater in, switch the heater on and set its themostat to a high setting. The digital t/stat will then control the heater.
I was a bit disappointed that the minimim setting on the t/stat was 45F, but it has worked very well. I had a Kill-a-Watt meter in line with it and it didn't do a great deal of damage to our power bill. I've had the wireless remot temp sensor in the rig, and on nights when our outside low was mid 20s, the temp at the dinette table was about 38.
BTW, I got it from Amazon.com. It was about $36 including shipping.
Frank and Eileen
No longer RVers or FR owners