Big Ed:
The answer to your question is as follows:
Your boat/trailer are covered by your policy for both liability & physical damage regardless fo fault or who the operator is at the time of loss. Of course your deductible will apply.This is both on & off the water.
Now if someone else is towing your rig and is involved in a collision their auto insurance will be primary for liability, Physical damage to the boat/trailer combo is still on your policy.
See the article from last season on insurance.
http://www.wakeworld.com/Articles/2004/insurance.asp Hit me back if you have any other questions.
Rick