Camping with a 5th Wheel in Yellowstone Park

Does anyone have experience with camp site availability in Yellowstone Park? According to the Park web site it doesn't appear that they can accommodate anything of size. I have a 35 foot 5'er and my truck is 20 feet. We have camped in Yellowstone in small rigs before and I swear I remember seeing a lot of larger 5th wheels parked in the camp grounds.
Thanks for any any input.