Maps will help with your planning.
As well as the excellent advice above - car and motel are definitely cheaper than motor home, and a lot less hassle when you are in urban areas.
What I suggest you do is, since this trip is still three months off, you get hold of some good detailed maps. If these are not available locally (you don't say which State you are in) I can recommend you get a Rand McNally road atlas from the RTA store via the link at the bottom of this page. The maps in this popular directory are in great detail showing all natural and historical attractions as well as touristy and more. They also grade the roads - from high speed interstates to local and back roads, and highlight scenic routes. All the sort of information you will not get within the confines of a little screen. If you order it now you will have it in a couple of weeks.
For affordable car rental try some of the consolidators. We hear at times that they waive some of the additional charges. A member from Brisbane used them on his last trip and was happy with the service.
Enjoy the planning and as questions arise feel free to ask.
Lifey