It looks like Paul and Roger covered it. Just a couple more things to add. My SOF is constructed as described by Putz, although I modified the design somewhat.

: Putz uses external keel and side rub strips. Looks like a nice idea, but
: something seems scary about screwing through your skin after you went to
: all the trouble to get it watertight. Does this make the boat leak, or
: does it seal pretty well with the screw pressure?

I placed a bead of caulk under the rub strips - just to make sure there were no leaks. It also served the function of giving the boat a clean look - the skin did not always lay flat where the deck and hull pieces overlapped.

: Putz skins the bottom and top separately, while the others are skinned with
: one big piece. Any particular reason?

Actually, after building one, I can't imagine covering the boat with one big piece. When covering the hull, it took a lot of work to get out all the wrinkles in the skin. I ended up with some wrinkles at the sheer line - which are now discreetly covered by the rub rails. There was just extra fabric, and it had to go somewhere. I really don't see how I could have continued it up onto the deck without those wrinkles becoming a serious issue. Maybe the problem was the modification I made to the design. The modifications were intended to make the boat more maneuverable and playful - and I am quite happy with it. But I gave no consideration to how fabric would fold over it - so perhaps that's where the wrinkles came from.

: Does anyone make these boats with bulkheads and hatches? Seems like you'd
: have to tie ropes to everything you stuffed into the bow or stern to get
: it out again.

I thought about that. The thing is that you don't want the skin to touch the ribs - only the stringers. So solid bulkheads are out. You could sew in a fabric bulkhead, waterproofed the same way you do the rest of the skin. Installing hatches would be pretty simple - no harder than installing the cockpit coaming, perhaps easier. I chose to skip bulkheads and hatches. Instead, there are eye-bolts at both ends of the boat with rope passing through them. I can now use the ropes to get things to the ends for storage and back out again.

: Maybe I'm overthinking this. My guess is all of these boats work! I'm
: probably going to adapt from both styles.

It's your boat - make it how you want it.

Good luck.