We are driving from Pittsburgh to Des Moines to rent a 28-32 ft. class C RV through RVShare.
For the OP, I'm curious about this part. Is this leg being included in the total amount of time you have available? Pushing hard, you can do Pittsburgh to Des Moines in a day -- but the rest of your family may not be as gung ho about it. Figure at least 1.5-2 days to do this, so that's 3-4 before/after you get the RV.
And what sort of vehicle is getting you there? Have you considered taking it along as well as your "free range" toad? A 2nd driver for it, spread the family out, and you'll enjoy your destinations a LOT more than having to drive the Class C around.