How about...

1. Under the house in the crawl space (depending on humidity, etc)

2. Under a shed or screened porch

3. Hang it horizontally on the garage wall (might even double as a narrow shelf for odds and ends)

4. Re-configure it (if possible) to be in sections, then lots and lots of options should open up

5. Start another boat, then storage becomes mute for a while

6. If you are storing boats on a rack system, perhaps you could suspend it by a couple of inches, below one of the racks

7. If you have a deck and don't want the strongback in contact with the ground, suspend it under the deck, and wrap it so that water dripping between the decking doesn't soak it.

8. Find a neighbor or friend who is having a storage problem of his own that you might be able to do something with, and work out an arrangemetn where you each store the others item. IE: maybe he needs a piece of furniture stored, and you have a spare bedroom that it would fit nicely in, and he has a perfect spot for your strongback.

Anyway, those ideas may not be worth much in your specific situation, but what the heck... maybe it will trigger another thought that might work for you.

Rick