The most likely thing to happen to your SIB is it - or the engine - being stolen from your garage or shed in the other 50 weeks of the year.
If you only want short term insurance, you can probably arrange it but it will be at less favourable rates. You would need to approach a broker.
I recently shopped around for insurance on a sailing dinghy and got the best service and a very much cheaper quote, from
John.Friendship@alan-thomas.co.uk I think this individual does the sailing boats and he may redirect a query about SIBs to a colleague. I have no other connections with Alan Thomas other than as a customer.
I worked in insurance claims for 35 years. Your household Contents policy is likely to exclude boats and their accessories. You need a dinghy policy to cover the boat and outboard (and anchor, etc.) against theft or damage when it is in storage, as well as against loss or damage while it is in use.