One way (there are others) is to place the money in an account that would require both the buyer and the seller to approve of any money being removed from the account. The account should be in trust for the dealer, to be released upon delivery of your boat or revoked upon failure to perform.
This should all be handled by contract. Have you spoken with the dealer to see what options are available from his company? A reasonable dealer will understand your concerns and work with you. If not, then find another dealer.
An attorney is recommended to at least review this type of transaction to protect your interests.
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Put it in a lawyers escrow account to be released upon completion. Also check and see if he could post a bond to cover your boat in the event he goes under.
Nothing in this answer is intended to be relied upon as legal advice and I make no warranties either express or implied that the information is accurate. Always consult a local attorney.