I have a 35' fiver. I stayed outside Devil's Tower NM but drove thru their campground (after I got set up) to see if I would fit. I'm pretty sure I would not. I did see one smaller 5er there but it seemed to be jammed into a site.
I'm just outside Yosemite NP right now. I just looked and they have 13 campgrounds, with 4 being able to take a trailer no longer then 35 ft. The other CGs max out at 30 ft or much less.
Sometimes the problem is just getting to the park. I just came from Sequoia NP. The drive to and inside the park is really twisty and windy with many really tight turns where it would be next to impossible not to cross the double yellow line pulling anything. I had no fun just driving my CC dually. I would not like to pull anything on that road unless it was a really short trailer. There were many signs on the road stating max trailer lengths.
The other times that this question has been asked, most folks seem to respond that 35 ft is about the max for most NPs.
I suggest you make some phone calls to the parks you want to visit and ask them.