Had my interest peaked in 4th grade school trip and have not missed a year going back since I am an adult, that is a lot of years. *S* Gettysburg Campground is a good choice but you may want to make arrangements sooner than later. We also like staying at Codorus State Park which is near Hanover, Pa, but about 25 minutes away. The state park has only electric hook ups.
Not sure of routes since I live an hour north of Gettysburg. You could find things to see and do in the area for a week, no problem. Some of my favorites, Visitor Center, LIttle Roundtop, Peace Light, High Water Mark. I am an avid cyclist so the area is great for bike rides as well. Be happy to answer any questions you may have. Enjoy