Had this happen in NJ once. Talked to the shop owner nad explained I did not hire you to store my boat, I hired you to work on it, and you not justified in collecting both especially since how long it takes you to finish the work is more of function of you/your shop, than it is me. If you insist on collecting storage, I will pay you what I owe, but I will also pull my boat immediately and go elsewhere. Owner agreed to waive storage.

I personally think it is one of those things that somes guys do just hoping that a few customers will pay without balking, if they balk, it goes away.

I could see storage charges only if any delay in progress is caused by the boat owner.