I have been to Indy several times over the past 20 years. The last few visits were for the USGP and 500. It is a bit of a different ballgame for RV'ers. If you are heading there for the 500 or the Brickyard, just expect that there is going to be A LOT OF TRAFFIC AND CONJESTION. My recomendations is to just plan on boondocking it and stay very close to the track. Traffic coming into the track area and parking lots are slow moving and really not convenient.
The 1st recomendation is the Coca Cola field across the street diagonally (Georgetown Ave.) from turn 4. It is flat, grass, and always full of rigs. No electric, no hookup's at all. You can easily walk to the gates at turn four or further down the front straight. Word of caution, walking anywhere around the speedway is farther and longer than you anticipate. On hot days it is easy to tire even if you're young and in good shape. There will be people everywhere and constant traffic on the streets.
IMS had bought the small campground just outside of turn 4 (used to be private), but I do not think they allow big rigs there, but worth checking.
There is RV parking across from track parallel to Georgetown Ave. We stayed here the last visit, but had no hookups, but it seemed that some of the spots did, again, easy access is a plus and ease of walking. (You can take small coolers inside, as long as they can fit in the footwells of the stands).
There was RV parking in paved lots across 38th St., but again, as this is commercial property, no hookups.
Also, since the Speedway sits adjacent to a housing nieghborhood, many of the homeowners along the 3 or 4 block area allow camping in their front yards, back yards, side yards etc. We did this one year ($75 a night)
I guess my point is this, if you stay at a campground nearby, you may have the luxuries of electric and water, sewer, but, you will trade it off in the inconvenience of battling the other 350,000 folks trying to do what you are doing. Believe me, it is a lot of people. Wait until you get inside and look at the full grandstands, an incredible amount of humanity.
All that said, make it a must do. I tell people that attending the Indy 500 should be on everyones "Bucket List". The sights, sounds, colors, smells and ramped up excitement is just unbelievable, even if racing isn't your sport of choice. You should plan on getting there no sooner than Friday evening (sooner if you have a lot of time to kill, you may get a better chance at closer-in parking). There is little to do other than the Museum (Yes!) and the track bus tour (ok). The rest of Saturday is usually taking in the hundred or so merchants lined up and down Georgetown Ave. (Carnival like) Lots of food and race stuff. If you have your toad, I would recommend one other opportunity while you are there. Head out to Oreilly Motorsports Park (formerly Indianapolis Raceway Park IRP) on Saturday night to watch the "Night Before The 500" midget races on the half mile asphalt track, within 10 miles of the Speedway, great fun and the midgets are very exciting to watch.
Here is another little piece of good advice, depending on how many are in your group. In all my visits to the Speedway, I only bought tickets ahead of time once, and would never do it again. There are literally dozens of ticket "vendors" walking up and down the streets around the speedway. I have learned to wait until raceday morning to buy my seats. I have never had any problems with this, and have sat in some of the most expensive and best viewing seats in the house! Usually at a fraction of the face value or Saturday price. Yes, it takes a bit of nerve holding out, but you can save a lot of money, and if you do your homework ahead of time, find really great seating. Always stay as high as you can afford to get the better view. The only pitfall to this is if you need 5, 6 or more tickets in a row, you may be a little more limited in selection, but then, that many over two rows together would probably be quite possible.
Hope this helps a little. DO IT!