You can do the GSP with that height. I'm assuming your first stop is Timberlane in Clarksboro?
Here are the alternates I've actually done. You'll need to check the availability of CGs open year round.
Mass Pike to I-84 to Scranton then I-81 to US17/US50 for Fredricksburg VA. The Fredricksburg KOA is open all winter. You'll need to find an overnight around Harrisburg.
Mass Pike to I-84 to US209 to I-80 to I-78 or directly to I-81 then as above.
Your route around the bend on I-287, but pick up I-78 to Harrisburg then I-81 as above.