Tony, I thought of adapting the porta potty seat in some way, but after mulling it over, decided to forget it as it would have been much more work, for a less comfortable seat.
Re: those IP pics: Cool!!! Pics which show just what I was talking about with the IP chainplates...
Here's my extra chainplate explanation:
Ebb, everything in this pic is plastic and glass, no metals at all:
Attachment 6706 (<--- also at bottom of this post, attached to Tony before)
A bolt will come through the hole in the middle, from outside, that holds the chainplate. It'll have a big ol' washer or two on it, and a nut holding the whole assembly in place. The FRP thingamajigger is purely there to spread the load from that bolt coming thru the hull; to change it from a point load of vertical shear in one small location, by spreading the stress down and out onto a large area of the hull.
There will likely be two 1/4" layers of solid FRP located on the inside of the hull at each chainplate, one layer against the hull basically the same size as the chainplate, and then a row of these tabular things bonded to that which will help the FRP rope grip against the shear via a wider radius than if it simply wrapped over a bolt.
Put in the big piece against the hull, attach the smaller tabs, fair it all in with resin thickened w/colloidal so that the rope over the tabs has nice straight runs down onto the hull. Use that rope to spread the vertical shear stresses out over several square feet of hull surface, instead of just right there at the 'plates.
Here's a visual attempt at explanation:
Do dat make mo sense?