I have a 280RS, just a little over 30ft. I find that when trying to reserve spots 29 seems to be the cut off on the filters for many NPS campgrounds. In the last 18 months we've visited several national parks, but stayed in few. We stayed at a USFS campground outside the Grand Canyon, could not find space inside anyway.
Went to Zion in April but stayed outside, no space inside and when we drove thru we determined that we would not have fit anyway. Stayed 3 days at Lassen Volcanic NP in November, managed to get into a pull-thru but it was a tight squeeze. Had to trim some tree branches. We stayed at a state park near Olympic NP, again, driving thru the park we would not have fit into any site. And it isn't just the sites, but roads can be very tight also.
Some of the WA and OR state parks are good for size, like Cape Disappointment and Ft. Stevens. But there are some that are very tight, especially ones in more forested areas.
California state parks, especially older ones, we don't fit in. We drove thru Castle Crag SP but would never take my trailer there. Spent a week at Lake Perris SP up in the dry loops. The FHU sites are too tight to get into. There is literally only 1 site at Leo Carrillo SP that we fit into.
Have stayed at lots of AZ state parks, they are nice and have had no issues. NM sites also are ok. TX state parks are mostly older but we've been to several and managed to fit. Caprock Canyon was easy, Palo Duro Canyon has several CG's, the Hackberry loop where we stayed was a little tight, Juniper looked better.