Before anyone says anything, I know you don' t put both your feet in footstraps at the same time. I'm just allowing for a one-time install that will let me adjust and find the best spot.
OK, so the beam bolt is easy, what about the one to the deck? I would like to have an aluminum backing plate to spread the load along the hull, but that would require installing an inspection port on the stern. I have seen them on many other boats but I'm afraid to do it on the 15. The smallest port I have found is 3.5"
The aluminum backing plate I have is a piece of an old Nacra dolphin striker.

I have some toggle bolts, but they require about a 1/2" to 3/4" hole to get the toggle part through and I don't trust the durability of them, especially in a salt water environment.
I also know that the straps will be used to pick up the boat. It is just inevitable that someone will do it because there really isn't any other place to grab on to.
Does anyone have a better idea?
Bill--what say ye on the ports?