In PA the gravel floor will work quite well, I'm in the process of laying down brick over the gravel now so I will still have a porous floor.
FYI there is a gas heater that will run completely without electricity. DM me for the brand name.
My power rarely goes out, but a power outage in the summer would be an issue if it lasted very long, I have considered buying a portable generator just in case.
I spent a good year doing research and planning which paid off in my situation.
If you ever are passing through Easton PA give me a heads up and I'll give you the tour.