Ovey, I can give you some more general pointers (this is from me personally as a boater and a buyer of insurance).
Generally all policies have similar coverage, but you need to look carefully at what is excluded or limited (e.g. geographical cruising areas, wear & tear, underwater parts, security & anti-theft requirements, fire precautions etc).
I would take photos of your boat in storage if kept on a trailer, showing clearly the fitted wheel clamps, trailer hitch locks, engine locks, and all other security measures including close up pictures. Also if you move the boat/trailer and store is somewhere else for a short period use your phone to take a couple of quick pictures once it is locked up - only takes 1 minute and hopefully will never be needed.
Should you be a victim of theft or attempted theft, then you have clear photos showing the precautions you have taken. Engine locks are usually always required and it is important to prove they are fitted, and keep receipts for purchase of them. Worth checking what the policy wording says about this and you would be well advised to discuss this with your insurer to verify that all the security devices you are using are accepted by them.
Coverage for machinery items and underwater equipment (inc props) can vary, so worth checking what is provided.
If you intend to leave a trailered boat on moorings overnight unattended then you should enquire about that also, including the amount of time it should be left unattended.
Be alert to areas where thefts are occurring as there can be hot spots. Posts on here and entries on stolenboats are handy to keep aware of. Some places seem to have more reported thefts and may be worth avoiding or taking more precautions.
Valuations for replacement parts, engines and entire boats can vary. An insurer may use the Three Stokes engine price guide, market values, price originally paid, or a combination. So also important to understand if you suffer a loss how would it be dealt with to put you back in the position you were before the incident, and you need to satisfy yourself that you are not under insured. Older outboards can be difficult to replace if an insurer relies upon heavily depreciated 'book' values.
Trailers, engines and personal effects (stuff you would not ordinarily sell with the boat) can be separately listed, so make sure your amounts listed are adequate.
If you have time you could trying speaking with the claims section of whichever insurer you select, and run through the potential scenarios that you may face to see how they would respond in general terms, and that way you can see now if you need to change any kit or ways you do things.
The cheapest possible quote may be a false economy in the long run...