Not sure why you specified no basement, but after having a cabin on piers and a couple of houses with crawl spaces, I'm hoping to either be on a slab or have a basement in my next place. I'm tired of crawling around in cramped spaces to do work on systems.
Functionally, it sounds like either a crawl space or a basement would work well for your place. Once you're going crawl space, IMHO, you might as well just make it tall enough to walk around down there. Don't know enough about FPSF's to know if that's a good alternative or not, but what others have said about the cons of slab heat for intermittent use makes sense. Might still be able to do one without a heated slab.
Even if you do plan on heating year-round, I still like zeke67's and others' ideas of making your plumbing quick-drainable. We had a place that was semi quick-drainable once, and it was nice to not worry about the plumbing over winter.
Not sure what the power dependability is there, but you might want to consider a propane backup heater if the power goes out. I have a propane heater that doesn't require electricity. There's a battery in the thermostat, and that will kick it on & off. That said, I know propane tanks in really cold climates can have issues that I don't have here in the PNW. Burying it might alleviate the issues.
After all that, if you're saying no basement due to water table issues, maybe helical piers are a possible solution, but then you're looking at exposed water line going in. Not sure what the options are for keeping that from freezing. That's my food for thought ramble.