Finding a Camping Spot During These Peak Travel Times

The only time I made reservations was this Summer was on the Oregon Coast. And that was only when we wanted to be at a specific rv park, at a certain time. Those reservations were only made
1-3 weeks in advance, at the most.
We have never, not been able to find a place to stay for a night or two by just pulling in somewhere, though, I have made early reservations for a couple of months this winter already.
We have a 33' fifth wheel.