I was able to just add it to my homeowners policy per my insurance agent. I'm paying around $170 per year!! He also handles my truck, motorcycle, and business insurance, but this was his best guidance........hope this helps!
We did the same thing last year with Pemco - a Washington State carrier. The 'Mariner's policy was added to our auto/home coverage; agreed value for our '77 E35II: $25K. Full hull/liability/medical coverage with some elected exclusions: $205 annually; discount for licensed (safety course) mariner, good FICO score, driving record, etc. No survey required.
Downside: Pemco only writes policies in Washington. We're planning a relocation, and having secured a slip, I needed liability/additionally insured coverage. Obtained it hassle-free on the internet from Progressive. Liability only, with good FICO/homeowner's discount: $88 annually.
Generally speaking, Progressive is arguably one of the best bets these days. Though I've never (knock on fiberglass) had a claim, and can't speak to their remuneration services, I wouldn't hesitate to recommend 'em.
Not affiliated with any company, and your knot speed might vary.
Capt Dan G>E35II "Kunu"