Hi Dave, I had the same problem several years back. Agua Verde http://www.aguaverde.com/ on Lake Union had some limited space. There is outdoor storage under the South anchorage of the University Bridge - I can't find/remember the guy's name but ask around at Aqua Verde and Enetai Beach - that's how I found him.

I ended up hanging the boat outside under my car port. I put a deck plate through my rear bulkhead so I could lock it up.