Easy answer: reduce heating costs by turning down the thermostat and wearing heavier clothing. Try some mild calisthenics - the body is great at generating heat, turn sugar into btus.
Homework: Determine which costs more per kwh (or btu), propane or electricity in your area... then use the cheaper option for heat, supplementing with the more expensive option.
Extra credit: find a park that doesn't charge based on usage - I've never stayed at a park that charged extra / separate for electric, but I've never stayed anywhere more than a week at a time.