For the North Rim of the Grand Canyon, I'd recommend either
Kaibab Camper Village(looks tight but a log of bigger rigs get in there as we have) or the
Forest Service Campground at Jacob Lake. You can zoom in and determine if you'll fit. Most likely you will. Google this CG and you'll find photos.
As for Yellowstone. Only one in the park, maybe two, will fit your rig (in my opinion, others may differ) - Bridge Bay or Fishing Bridge. Outside of the park there are numerous possibilities if you don't mind driving in, even long drives. We've stayed at Colter Bay RV. Colter Bay off Jackson Lake on the Rockefeller Causeway has an RV full hookup side and a dry camping side. On the other side of Yellowstone, in West Yellowstone Montana is Grizzly RV as one person already said, but there's also Baker's Hole, a FS CG with big rig sites, E at most sites and water to fill at the entrance. The only draw back is that it's first come, first served, but in my opinion, well worth it. We've dropped our rig off at Grizzly, driven over to Baker's Hole and checked with the host as to which sites will come open in the morning. We then check them out and drive over the next morning, put or name on one, pay, then go back and get our rig. It's worked out well for us this way. There's also a nice RV park out further by Henry's Lake on the Idaho side called
Red Rock RV. We've stayed here a couple of times and have really enjoyed it. We don't mind driving so it was perfect for us. We've also stayed on the Wyoming side off the Togwotee Pass at a FS CG called Falls. One loop as E and big rig sites. We've stayed there a couple of times, driving into Yellowstone for the day. We're the type to get up early, pack a picnic lunch and head out, returning in the evening. Other's are different. Here's a photo of our site at the Falls CG off Togwotee Pass -
Here's our site at Baker's Hole -
Here's a picture of Grizzly RV -
Picture of Colter Bay RV - looks tight but long Class A's get in here easily -
