Experience from a few months ago:
I found Kodachrome Basin SP to be an excellent value for visiting Bryce. The FHU commerical campgrounds inside Bryce (or any providing electric for that matter) were closed when I visited in December, but not Kodachrome. Middle of December, temps in the teens, they were open and had nice pull-through sites with water, sewer, electric. Probably harder to get a spot now, but worth a look. Long drive to Zion however.
I stayed at the fed park in Zion, content with just electric. Tried to stay at a FHU just outside the park, campground was part of a Holiday Inn or some other chain hotel. The campground was out of business at the time, despite advertising being open year round (including the sign right outside on the highway) - who knows if they've decided to reopen or not. I think they were maybe converting to a trailer park? Lots of trailers inside looked like they're permanent residents. (Skirting, park-model trailers, etc)
