How about a quick-release setup on the beam bolts? Maybe something similiar to bicycle hubs. You could reduce slop in the the joint by putting a dome or slot on the hull and a complementary dome or slot on the crossbeam. With a quick release cam fitting, you may be able to get a good tight fitting without all the hassle of regular bolts.

I don't have a patent on this, so if anyone wants to take the ball and run with it, be my guest.

David Ho
TheMightyHobie18 1067