I only had one come apart and go back together without having some issue with the stainless bolts that go through the hulls and into the crossbars..( You can read about these issues elsewhere on this forum) They thread deeply into blocks inside the crossbars and the threads "gall" very easily, and/or crossthread.
It's critical that you install the crossbar bolts with an anti-seize grease applied to the threads. Otherwise, the threads will gall causing the bolt to get stuck in the crossbar. You should get all four inside bolts started before installing the outside bolts. Also, use only hand tools to install the bolts, it would be very easy to cross thread the bolts if you use power tools.
I've never had any major issues getting the 18 to come apart or go together, but it is a little bit of a pain. I highly recommed that you strap the hulls to the trailer before installing the crossbars, that way they don't fall over while you're trying to get the bolts lined up.