When you see such limitations listed on a NPS web site - it is a very good idea to plan to drop the trailer in a parking lot, and drive the road. Only you can determine if your rig can make the drive.
We hosted at an NPS campground with such a limitation. We had no trouble making the drive up the 12% grade and the seven tight switchback turns pulling our 36' trailer in our 22' long pickup.
However, I would not try to go to that CG for a visit because while there are a few sites that can/ did hold 32 ft long Class C rigs - none but the host sites could hold our rig. Even then, I had to back the rig about 1/4 mile uphill to get out of the CG. There wasn't a loop that I could get the trailer around the tight turns.
As far as getting an answer - maybe 1% of the people you can reach on the phone know anything about RV travel and needs.
Some great people work at NPS, USFS, COE and State Parks - who have never pulled a trailer, driven a Class C/A, never actually camped in an RV (or a tent).
They really don't know what you need for clearance. I've seen places my 36' TT can clear on campground turns, but a 32' 5er cannot because it tracks farther inside the turns. I've seen places that my 22' long truck cannot make the turns, but an 18' short bed can.
