Another thing to think about.. The last National Park I have been to was Grand Canyon (South Rim) many fine commercial CG's just outside the park but the one inside the park.. Well no way on earth can I get my 38' A in there and I'm good at "Squeezing" as it were. Heck I was a bit uncomfortable with a car.
AND.. IT IS A COMMERCIAL campground. Operated under a lease agreement by a "Vendor". so my "Geezer's Pass" not honored.
(Not a problem since I left the A in Page AZ)
Not all National Parks even have a campground. However there may be a State or Private nearby. Hiawatha National Forest is an example of such. And I might add a lovely chunk of woods. Been there.