Rolltider,
First off, A 600 mile day is a 12 hour road day.
Unless you have multiple drivers and your coach is pleasant enough for one to sleep underway, be aware that a 600 mile day is tough. And you are betting on three in a row.
We have done this. We don't when we can avoid it.
Train both kids to be navigators, that takes a lot of load off the driver.
There is no longer any good stand-alone planning software that can be used to navigate underway. But grab up the demo package of RV TripWizard and fight it to your plan. It will be pretty good, but it will also be an eye-opener.
Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.