"There are no hookups sadly" Just the opposite that is truly boon-docking and the best get-away! Unless traveling across the US we never hookup, nor do we go to a structured camp ground.
Without the heater the propane will last a very long time. probably most of the summer. The heater draws the most propane.
You will hear a lot of ways to check your propane. I hope this does not derail your thread but I think it applies. Once in a while take some very cold water (hot in the winter) and pour over the propane bottle, quickly feel down the side for a temperature difference, that is where your propane level is. I agree with Lwiddis that if you only have one bottle go buy a second.
Enjoy your no hookups! Very exciting.