where to for a month. Gettysburg, etc

Well, our plans to go out west from Florida this summer fell apart due to a family thing. Sigh, maybe next year.

Sooooo......change of plans.....we are looking to explore the east coast again this summer (we did a month at Williamsburg last summer and it was great, we love history). Anyway, We were thinking about exploring the Shenandoah valley up to Gettysburg, and maybe to Hershey. Our previous trips have worked great at finding a good campground in the middle of things, paying by the month and exploring out from one location. This is by far cheaper, half as much as paying by the day and moving a lot. However.....this trip seems too spread out. I don't know if a single base camp will work.

Any thoughts on this trip? Should we look for a good base camp for this area...and if so, where? .....or should we move around? If moving around.....how long in what areas? Should we book a week in Gettysburg and one in Hershey? What about Shenandoah valley? Where to spend a month? ??
Oh, and we are two retired folk, no kids and we RV to sightsee.

Any help is appreciated. We've never been to this area before. Thanks