Welcome to the RTA Forum!

With the amount of time you've got available, and the list of things you want to see, have you considered flying out west - and just doing a loop from say Denver or Salt Lake City? If you are going to rent an RV anyway, I suspect the costs won't be all that much different - especially with the one way drop fee on the RV. That would give you quite a bit more time to get to all he places you want to see.

Otherwise, the order of your trip would probably be Fly into Phx or Vegas, then Grand Canyon, (other Utah Parks?), Arches, Tetons, Yellowstone, Rushmore, Badlands, Home. You could just as easily do it in reverse, and I'd say the cost of the airfare and rv rental would probably be the most important factor there - as it could be quite a bit different depending upon the direction.

As a one way trip, it would still be possible, but with 7 places to visit, and about 6 days worth of driving, you wouldn't have time to spend more than a day in more than one or two places - with the note that Yellowstone is so huge you really need a minimum of 2-3 days to see the highlights.