Every National Park measures their campgrounds differently. A lot of the time a campground maximum length is set based on roadway restrictions. A good example is Mount Rainier. Individual campsites might take a longer vehicle, but the ability to get a trailer around right spots in the CG restricts the maximum size.
I’ve pulled a 39’ TT (tip of hitch to rear of sewer tote carrier) with a 22’2” long pickup across 46 states and 45,000 miles in 4 years and 5 months. I’ve been able to get into almost every CG I’ve wanted. Of the NPS operated CG I’ve visited, most are National Monuments not National Parks. Frankly, I stay a lot more at COE federal campgrounds, BLM and Forest Service than NPS parks.
The biggest hassle is hooking up/ unhooking. I often travel with friends with Class A units. They are always faster/ spend less time than I do. Of course they have automatic levelers, I don’t.
Since sites with hookups are very rare in National Park CG, I also have to unload and setup my generators. Theirs are built in.
I would consider any pickup less than a 250/2500 inadequate for the type traveling you are considering. Diesel if you can afford it.
My preference if I was starting this journey over would be a 30-35 ft Class A. A small diesel if possible. We had a car that would have been a good toad, but we sold the 30-35 mpg potential road to do 35-45,000 miles of day trips a year at 13-16 mph in our 2500 pickup.
When I get near cities in many states I find the pickup size limits where we can go and what we can do/ see more that the trailer size.
As mentioned above, it is all about trade offs.
Another key is how much of the year you will do this. It is one thing to take a nice sized trailer out to a favorite boondocking site three or four times a year.
Completely different to spend 85 days in Utah, moving 20 times. 20 times setting up the generators and solar battery charger. 20 times tearing them down.
