When we stayed at Grand Canyon MP several years ago, there were a number of LARGE class As there. Ours is just 30', so we had no problem, but there was a 45' Prevost pulled in next to us with no trouble at all. However, there was another big one that came in after dark, and ran over the power post, and a couple of picnic tables. He dug one of the tables around a bit, doing some damage to the rear of his rig. Saw him leaving the next day, with parts of the table still hung on the rear, and a lot of sheetwork damage. Last year, we spent three months at Hot Springs National Park and stayed in the park campground. It has been reworked, and has ALL 50A FHU sites, but has no bath houses. Many big rigs were there, but not all sites will support the bigger ones. 40' did not seem to be any problem.