If you are looking to just plan an itinerary on your laptop or PC you can use Tyre which is a free download and will allow you to create a route. It uses Google maps and you have the ability to switch to street and earth view for a close look at what to expect the roads it chooses for the routes to be.
If you want to use Streets and Trips on your laptop with its optional GPS usb receiver while you are driving following the route you saved, then many like Streets and Trips. You can purchase it wherever Microsoft software is sold - Best Buy for example or Amazon online. We have tried both Streets and Trips and Delorme's Street Atlas which comes with a usb GPS receiver and we like Delorme best. It has a feature that allows you to use the built in microphone in the laptop to ask questions about the route as you drive and get answers - "how long before we arrive?"; "where are we now?"; "what is the next turn?" and the like. Streets and Trips does not do this.
None of these will route an RV on routes avoiding hazards to an RV for example they do not route taking height restrictions, propane restrictions, or roads not allowing RVs into consideration. You may find yourself on a road on the route that you are not supposed to be on. For that you need an RV-specific GPS.