I have been staying in my Cherokee 284 BH for several months while I work away from home. I have a radiator style heater (oil filled) that does a good job of keeping my camper 68-70 degrees inside. My gas heat (thermostat set on 67) comes on about once a night when the temps get in the low 30's. I have the winter package which has the underneath sealed and insulated. I still open the cabinets where the water is located at night. I have my electric heater on a timer. it comes on at 5:30 PM and cuts off at 10AM. I have a light also attached to the timer so I can check at a glance to see if the timer is working. It took a while to find a timer with three prong outlets. Depending on the size of your camper, I think an electric heater would be a good solution. I got mine at Walmart for under $50. Its basically the same heater that HSVBamaBob listed except it doesn't have the thermostat.
2013 Cherokee 284BH
2005 F250, 6L Diesel, Lariat, Quad Cab, 4X4