If you need to stop somewhere around Harrisburg, PA go a little northeast to Twin Grove RV Resort and Cabins in Pine Grove PA. www.twingrove.com
It is a former KOA that has been fixed up, it has wide, grassy pull through sites. The people are extremely nice and helpful. It is about 20 miles to Hershey if you want to visit. We stayed there 3 nights in April with a 40' MH towing our Saturn and had no problems with access. Do not stay at the KOA at exit 90, it is an overcrowded dump and at least when we attempted to stay there, had bad power pedestals Attachment 125396
and only 30 amps, all the 50's were occupied even though we had a reservation for a 50.
For Twin Grove take exit 90 off I-81 go east 1/4 mile, turn left (north) 7 miles on route 72 and 443 to the campground. The resort is surrounded by a state park. When you go to leave you can continue north on 443 and rejoin I-81 at exit 100, that way you only go about 3 miles out of your way. We found Twin Grove by accident and are very glad we did, we will definitely make it a stop on our way north or south in the future, you will not be disappointed.