I prefer I78 from just north of Harrisburg to 287 to 87 to 84 or 90.
This is the route we take if we go south and take 87/84/90. Going straight up to 90 on 87 is a little longer but less stressful. In all honesty, though, if you want to avoid wild and crazy drivers the northeast isn't the place for you! We like Poland Spring campground, but it's about 35 miles outside the city, and the last time we were there, not completely big rig friendly. However, they were working on upgrading some sites near the main road to allow for some larger units. We were able to get our Endura in there without much difficulty.