You might get the impression from a couple of posts here that you can "see Yellowstone in a day." Remember, these are locals, who can visit frequently. You're coming from Iowa, and will want to see more of the park than you can "do" in a day. For that, you'll need camping. I "third" the recommendation for Grizzly RV in "West" (i.e. West Yellowstone) - it's close to the west gate of the park, is very nice & clean, less expensive than the KOA west of town, and has sites large enough for most RVs and trailers, all with full hookups. Showers, laundry facilities, and close to town as well, so you can conceivably walk to the tourist shops & restaurants.
If you don't need hookups, there are several CGs inside the park. Madison seems to be the most popular, but Bridge Bay, Canyon, Grant Village, Norris and others can accommodate RVs up to about 25'. (Most national park CGs are older and were built long before today's big campers came into vogue.) All but the smallest CGs (with the smallest sites) are reservable and you NEED reservations quite far ahead.
I agree that you should plan to spend at the very least one full day in the area touring Grand Teton National Park, which virtually abuts YNP to the south. Depending on your schedule and your tolerance for long-distance driving, ideally I'd recommend spending a minimum of 3 full days in Yellowstone and and 1 in GTNP, plus of course partial days when you arrive and leave. If you can plan at least 2 more full days in the area, so much the better.