A timely thread! We're planning a trip to Maine this year. I'd seen Baxter SP but didn't think to see if they had restrictions. You saved us an unpleasant surprise as sounds like we won't be able to enter with our dually much less the TC. As stated though, there's plenty of other wild areas of Maine to visit and the wildlife won't stop at the state park boundary signs.
I did determine that much of the wild area of Maine is highly regulated and actually somewhat expensive to visit as can be seen at this website:
North Maine WoodsIf I was able to spend a lot of time there it might be worth purchasing an annual pass but I'm still on a payroll so won't have time to linger. My guess is the rules are a purposeful way to limit outsiders and reserve the area for locals. It is private land and privately built roads though so I don't have a problem with that.