Don't know what RV you are using, diesel or gas? I start my long trip planning by just using a regular map on my laptop. My I-phone has a Pilot Truck Stop App with a trip planner that works really good. I use that for getting my miles between two points, plus it gives me all my available places to fuel.
We never do "RV poker runs" like you are planning. We keep our miles per day between 250 and 325. I like to hook up around 9am and get off the road by around 3 or 3:30pm. But we are full time and retired. I understand you have a deadline and destination to make.
You will beat yourself to death if you attempt to travel 600 miles per day in an RV. But if you think you want to try it, then pick a good safe looking Walmart as an overnight stop. It will be easier stopping and sleeping there at 8pm as compared to trying to navigate a strange campground late at night.
I would try to keep my miles per day down to 400. If you want to get up early and leave each day you can still make your destination before dark probably.
2014 Montana 3725RL (Goodyear G614 Tires, Flow Thru TPMS)
SPENDING THE WINTERS AT OUR HOME IN SW FLORIDA. THE REST OF THE YEAR SEEING THE U.S. FROM OUR LIVING ROOM WINDOW!