Sure it can be done, at least part of it. We did Yellowstone in our 28 ft coach last summer without a TOAD the week before the big solar eclipse. Parking at Old Faithful was possible, it is a giant parking lot, though we did end up about as far away as one could be from the geyser parked in 2 regular spaces end to end, not a designated RV spot. In general we were able to get into most of the RV accessible parking lots to see attractions, though some of them required circling through at walking speed multiple times to find a parking spot, people in cars were making their own parking spaces along the entrance to the parking areas and even on the edge of the main loop road. The one major exception to this was the Geyser Basin area just north of Old Faithful, this area had cars pulled off on the side of the main road parked over half a mile from the pull off points for designated parking. Other areas like the Canyon rim drive loop we had to take 3 times through the one way 2 mile long loop before managing to get any of the RV parking. The Geysers at west Thumb was much of the same, looping through the packed parking lot repeatedly waiting for a space to open up, this was not an RV only thing, people in cars were doing it too, of course there are far more car spaces than RV spaces. Also the commercial tour buses also hog the RV parking spaces, using coordinated blockading actions to save them for the next commercial bus (something I think the park rangers should not allow).
