Dave,
If you are interested in Yellowstone, get the maps now and start studying. There are numerous campgrounds in the park, but the only FHU is Fishing Bridge. It is not cheap, but nothing there is. The other FHUs are private and outside the park. If you will use the generator to recharge the house bank, as said, it has to be quiet.
Get the maps because the park roads are essentially two loops. Each with many stops. There is a lot that you can see from the road, but there is even more that you can miss from the road. Last time there about a year ago, I was lame and could not do more than a couple of miles a day on foot. There were things I wanted to get back to that will have to wait until next time.
Even if you can't do any serious hiking and will just drive the two loops and some side trips, it is still a three day deal.
Matt