That was definitely the plan. Luckily, there seem to be plenty of RV sites available in the park during our timeframe, so we're going to have that ironed out before we do anything else.
Let me just say...I ADORE Yellowstone. I got a chance to work there as a researcher for 8 weeks, and it was the best time of my life.
HOWEVER, I had visited YNP three years previously, and it was the WORST trip of my life. Why? Because I went in the middle of tourist season, stuck to the roads, and had to battle the horrid "wildlife jams" and idiot drivers.
Yellowstone is an amazing place - IF YOU GET OFF THE ROADS. Go backpacking, for crying out loud. Go for a hike. There's some statistic out there that says some ridiculous percentage of people NEVER leave the roads or the easy roadside hikes (like Old Faithful, some of the geothermal pools, Tower Falls, etc.) - and the real magic of Yellowstone is away from those places. Overnight backcountry permits aren't too expensive, you won't have to compete as much for campsites, and you get to enjoy a piece of the park that people rarely see. Of course, you have to be in somewhat reasonable shape to do this, but some of the backcountry sites aren't that difficult to get to - you just need to make sure you have the right supplies, and are smart about bears (there are a LOT of them - that's what I was researching).
But all in all, ENJOY! And then go to Glacier National Park, it's much, much awesomer. And the glaciers will be gone in a few years.