I worked and took groups (grad students) through YNP and Grand Tetons NP for the past 23 years. The roads have been under constant construction and upgrade each summer. The south loop has been greatly improved, graded, straightened, adding width and berms. Parts of the north loop has also been worked on, but there are areas, like north of Tower Falls on the east side of the north loop, and the hoodoos north of Obsidian cliffs on the west side that still have some narrow, twisting roads. Also don't drive out the NE entrance to Cooke City, MT in anything but a toad unless you have a very tight sphincter. Campgrounds in YNP that accept reservations are limited and fill up months ahead. The rest of the CG are first-come, first-served. They fill up by about 8 am each day. They are without utilities and are only for 30' rigs or shorter.
Travel through the park with a long rig and toad is very doable, but be aware to really see the park you'll need to find a campground outside the park and drive the toad. Pull puts are generally limited and tough to get in and out with an RV+toad. Visitor Centers are accessible by RV's but many people park in the RV spots with autos, making it sometimes tough to find spots you can drive in/out easily. Each night the park roads are full of supply trucks replenishing the various attractions, so the roads are of sufficient size.
To really experience Yellowstone, use your toad and take a hike. Over the years I've noticed few people ever get out of sight of their vehicle. Sad for them, but great for those of us who travel a little further down the trail suddenly finding the uninhabited wilderness Yellowstone has been noted for since 1872.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI