Where in the US are you touring?? It is wise to get a smaller wheelbase vehicle if you can as there are lots fo places (especially int he National Parks) that you cannot visit in a long wheel-based vehicle, so you miss out. Most of the RV camping spots in National Parks also have enough room for a pretty large tent. I would caution you on the type of tent you use as well. Your best bet is to get a dome tent of some nature that will stand up on it's own, without needing to be held up by guy ropes. If you visit the south west at all then you will often find yourself camping on sand or bedrock, very different to a grassy field at home. Hubby spent a very long night n the Valley of Fire trying to stop our tent collapsing as he had insisted on putting up our other tent (and wouldn't listen to his wife and put the dome tent up!!) he learnt that pegs in sand do not stay in for long!!!
Another piece of advice is do take into consideration how far you intend to travel and cost up the price of the petrol, so many folk forget that and find it to be very expensive. www.gasbuddy.com is very handy - it allows you to find the cheapest petrol in your area. We took out a costco membership as the fuel was much cheaper there and we could stock up on supplies too. Costco, Walmart and many other stores and Casinos allow RVs to park over night in the far side of thier parking lot (with permission) this can be handy to know if you have a long drive from one destination to another!!
Carefully check out the rental policy for all the hidden fees -- cleaning, emptying any tanks, additional gear, can often be extras taken as a matter of course from your deposit. so check the small print, especially any relating to mileage, some do a PER MILE fee above a small included mileage package, which can be stupidly expensive.
Also do check for discounts and coupons available for that company. And don't be scared to haggle, especially in this economy. On the off chance you are in the Armed Forces you should ask if they have military discounts, even though it is not US armed forces, UK is an ally and many honour discounts for UK troops too. If you have (or can get) an American Express card, you might be able to get their premium rental vehicle coverage.
Often smaller RV are classified here as Class B.
Have a couple of ideas for you of some companies who are good:
www.roadtriporegon.com
www.vwsurfari.com/
www.californiacampers.com/
www.leavinglasvegascampervans.com/
Hope that helps. :)