I would think this is a very high priority location give the proximity to Baltimore & Philly and half-way point between existing Somerset SC and soon to open Allentown SC.
Just speculation, but here are a couple of good possible locations, pretty well centrally located and near both east-west and north-south routes. There are multiple businesses and hotels in each area, some hotel chains where Tesla has already installed SC's in other areas of the country:
Harrisburg Mall, 3501 Paxton St, Harrisburg, PA
Hilton Garden Inn, 3943 Tecport Dr, Harrisburg, PA
Holiday Inn, 4021 Union Deposit Rd, Harrisburg, PA
Fairfield Inn, 1018 Briarsdale Rd, Harrisburg, PA
Sheraton, 4650 Lindle Rd, Harrisburg, PA