Thought I'd pass along a software recommendation. For several years I have used Tyre
(Trace Your Route Everywhere) on a desktop PC to plan motorcycle trips. The usual goal for bike routes is, the more crooked, the better. Not exactly what an RVer might want.
However, Tyre can be used to lay out and evaluate RV routes, too. It utilizes Google Maps for its roadway data as well as Google's routing algorithms, both of which most of us are familiar with. After an initial route is plotted on-screen, you can drag-and-drop any part of it onto different roads.
You can turn on satellite view to scope out access for a parking lot or gas station entrance. Toggling on terrain view is helpful for seeing how hilly the route might be. And Google Streetview images are very useful for previewing roadway widths, gas station awning heights and pavement conditions.
Multiple routes can be open at once in separate tabs. Each route can be saved to your hard drive by name. Final routes can also be saved into a connected TomTom or Garmin GPS for use on the road. Or, of you prefer old school non-GPS navigation, you can print a trip book of your final route.
There are several versions of Tyre, but Basic Tyre is free. It does have ads, but they are not obnoxious. If you like it, there are paid upgrades available. Help is a available via a user forum, but the software is pretty intuitive. The developer updates it regularly.