Using a boat or a motor vehicle in a State for some period of time usually around 60 days other than for repair or storage allows that State to tax the if comparable sales tax was not collected in the state of purchase. If it was you get a credit. My buddy had his boat documented and delivered to Maimi. He ( a NY resident) kept the boat in NY. NY somehow found out.. He suspects a dispute with a summer slip Marina and the next thing he knew he got a tax notice. It took some doing to prove the present value was much diminished from the value 14 years earlier but he paid 8.5% on the fair market value to NYS.
Maine I think is 5.5%. Check the current value rather than your purchase price. You may not have much of an issue. I would advise that route rather than something regrettable.
Doug