From south Jersey it would make sense to pick up the Penn Tpke to I-81 in Harrisburg.
freecampstes.net lists overnight stops. Also, the allstays app for phones/tablets will show you everything; Walmarts, fuel stops, campgrounds, Cabelas, Cracker Barrels, etc.
I-81 mostly follows valleys. The highest terrain is south of Roanoke.
Jerry & Jeanne
1996 Safari Sahara 3530 - 'White Tiger'
CAT 3126/Allison 6 speed/Magnum Chassis
2014 Equinox AWD / Blue Ox