(a) MS S&T may not be the best tool to use, but it is _one_ tool folks sometimes use.
(b) I agree that's too much for a mere 30 days.
(c) I note that except for New Orleans, everything else is either pretty far east or pretty far west. I'd suggest you stick to the western end of things, maybe go SF to Utah Canyonlands, north to Yellowstone, then to Mt Rushmore and back. Death Valley in July is hotter than Hades when the devil is really mad -- you'll blow through there pretty fast. Or wish you had done so. It's starkly beautiful. But hot.
(d) Drivin' an RV is not like driving your car. You can't safely go as fast, because the vehicle is strange to you and nowhere as nimble as your car, you will have to pay much closer attention to what you are doing, so you are going to find it more tiring. Add in that you'll want to arrive for the night before dark, (both so you can SEE where to park and so the campground office is open when you get there) and you can't drive as long each day, either. Plan on 300 miles a day for a pleasant trip, and if you stretch it to 400 miles, your trip will be much less pleasant.
