We used to live in CT and travel to NE from NC often...our daughter used to live in Waterville ME.
We, too, have a 40’ 5th wheel. I suggest you get to I-81...no tolls which are expensive for anything above 7’6”! We pick up I- 78 in Harrisburg..some tolls on 78 but we want to avoid Scranton (terrible roads!). Then I-287 to I-87 to I-84 in Newburgh, NY. Some of these are toll roads but a smoother route. I-84 in CT can be slow going through Danbury and Waterbury...but once you get across the CT River it will go pretty quick on up to I-90 (Mass Pike). You can then either take I-290 through Worcester MA to I-495 to I-95 (at MA/NH border) or stay on I-90 to I-495 to I-95...you MUST have an EZPass for I-90/Mass Pike as it is now a cashless toll road.
We take I-295 through Portland ME. I would follow what previous posters say about getting from I-95 to Bar Harbor....