I would go down the river visiting the yards and marinas with the boat strapped on top of the car, asking about storing it. I'm a little surprised you're being told no, since a lot of the places have space in their racks, and others freely allow canoes and kayaks to be stored on the grass, chained to a tree. I would suspect they are thinking you are asking for real boat slips, which are at a premium.

However I would be very cautious about leaving a custom built kayak at any public or semi public area. This is a very unfriendly area, and I would expect your boat to be gone shortly if you do leave it at one of these facilities. Small boats regularly disapear from them. Many (most?) require you to sign a waver exhonorating them from liability as a result.

I'd more suggest asking a neighbor if you want free storage. Some of the storage locker places have some durned odd shapes. I used to rent a 5x5 locker, with about a 20 foot high ceiling for $25 a month in the DC area.

Lastly, if you're willing to come all the way up to Westminster, you can store it at my place.