Scot,

I built my CA Expedition with an internal box beam and my son's Parr with an external strongback. Both have their pros and cons, but I like the internal box beam a bit better. With an internal beam, you keep your "mold" assembled as one unit even after you flip the kayak over to strip the deck.

If you use an internal box beam there are several things I can suggest to make it a smooth and easy process.
1. Use decent plywood for your box beam; pick the flattest sheet you can find.
2. Assemble it on the longest flat surface you have available. Keep the part you're fastening on the flat surface. Also, I used spacers inside the beam to keep the dimensions consistent and to provide better grip for the glue/screws.
3. Build two stands for your box beam; this will give you four points of support. I built stands similar to the ones in Nick's book.
4. When you cut the rectangular holes out of your forms, be as accurate as you can. Next time I do this, I'll probably use a mortising attachment on my drill press for accurate corners.
5. Before you string the forms onto your box beam, put the box beam on the stands and make sure it's straight and untwisted. Most floors aren't straight or level so you might have to use some shims under the feet of your stands to get everything straight. When you get it just right, place some sand bags (or whatever you can) on the feet to keep them from shifting.
6. Finally, string your forms onto the beam. If you've done everything accurately up to this point, they should only take minor tweaking to align them perfectly.

It sounds like a lot, but it's a great feeling when you look down the forms and see them perfectly lined up. The plans you get from OOK are very, very accurate. If your beam is straight and not twisted you should end up with great results. When I put my forms on the beam they were instantly aligned; I only used shims to keep from pulling them out of alignment while securing them to the beam.

Good luck and post some pictures of your progress.

Pedro Almeida