JUst because you camped at four NP that does not mean that the 60 other NP sites and the large number of NM sites are all accessible. Some are some are not. Yellowstone is Fishing Bridge is a big exception since that is basically a big open field. We have also camped there several times plus Bryce, Lassen, GSMNP, GCNP and Big Bend. And we had a 34 ft fiver at the time. Yosemite has one CG in the valley that has 6 or 8 IIRC sites out of 100 or so that are big rig accessible.
And any of the big parks fill up rapidly after the reservation period starts. If you haven't reserved a spot for this summer forget about it. GCNP south rim may be an exception I don't know for sure.
So you need to plan way ahead if you want to camp inside parks. And in some cases even getting a commercial CG spot outside some parks is difficult. Yellowstone for example.