Cost wise, the weekends you don't use your seasonal spot, you are still paying for that seasonal spot.
We camped all over, and never did quite find that perfect campground for a seasonal spot. Seemed that the beautiful campgrounds with all the amenities had seasonal people who were not polite (for a polite description), and the campgrounds where we had the most fun had fewer amenities. Every campground had its pros and cons, and we couldn't quite find that one campground worth spending the entire summer at. We are still looking! lol
A friend of ours bought a park model camper for one summer for her and her kids. They enjoyed it and the campground for the summer, and the next spring she sold it. Worked out well for her.
I would suggest checking out different campgrounds before committing to a seasonal campsite.
