I just stated full timing this year so I only have 3-4 months of experience, but here's my .02
1. Know what the cost of propane is at your location and also what you will be charged per kilowatt hour of electric. My electric rate is .17/KW and propane is $4/gallon.
2. If it's really cold you will want to make sure you get some heat to the underbelly area to keep your lines and tanks from freezing. That probably means you will want to make sure your furnace kicks on periodically as it generally sends some heat to that area. If you primarily use elec heaters then you may want to somehow circulate the warmer cabin heat to those unheated areas. The problem you can run into is that if the elec heaters are keeping the cabin temp nice and warm, then the furnace doesn't kick on which means no heat is getting to your water tanks/lines.
I use an oil filled heater and really like it. I set it under a ceiling fan so that the warm air circulates better.