I would not trust progressive to do anything reasonable, should you have a claim. You may want to read up on their ex-CEO, Peter Lewis, an ultra liberal.
What they say they will do, and what they actually do in the event of a claim, are two distinct things, and unless you are an attorney or expert in Insurance law...the claim will be paid out in THEIR best interests, which will leave you screwed. Ask them specifically what they will use in the event of a stated value clause, to estimate the loss as opposed to agreed value or actual cash value...and in which state those definitions apply, or don't apply? They will use which ever state they pay out less...the state where the policy was written, or the state where the loss occured, or the state where the boat was "berthed"....again with out a lawyer or a lot of experience with insurance, you will be in a battle day one.
Personally, I would do without insurance, before using Progressive. They are that bad for any coverage, car/motorcycle or boat. When you advertise the lowest price, ever....you as the consumer will get the least possible anything -service/payout/coverage (read the fine print and compare it to a reputable marine insurance policy).