You're better off (imho) finding an insurer that will offer a fixed value, regardless of market value. E.g. if you think your boat is worth £10k you insure it for that amount & pay the appropriate premium. If it's stolen or a total loss, the insurance pays out the agreed value, not the market value.
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5