I assume you have a diesel engine. We have a 2001 National Tradewinds with a CAT engine in the rear. Our does have a block heater. Normally I use it for an hour or so when the temps get down into the 40s or lower.
There is a switch on the dash that turns the block heater on/off. Also if the GFIC plug in the bathroom area is tripped, our block heat won't work. Ours works with either shore power, generator, or inverter.
Just a suggestion--when you post a note, it would be very helpful to know what make of motor home, engine, etc. you have.
Lots of luck in your RV adventures. We have enjoyed ours over the past ten years.
Larry & Norma, Dallas, Texas
2001 39 ft. National Tradewinds LTC
2003 Suzuki GV ] PressurePro TPMS