It is important to check with your insurance company too. Many of them will only pay up if your trailer was locked onto your car. I know some insurance companies also specify that it has to be an approved trailer lock purchased from a store. Chains and padlocks don't count in some cases. Would be a double blow to have it stolen and then find out you're not insured when you thought you were. I think the lock rule might also apply when the boat is at home too.
Cheers,
Janelle