White pieces are fiberglass cut from a old jacuzzi, they are bomber, and gel-coat smooth.
Not sure if a bulkhead will be needed - just like Jan Dettmer said in a earlier post. Thigh hooks are simply duct-taped foam temporarily filling over factory kayak outfitting, at least until sure it's 0k to destroy (contact cement over) factory kayak outfitting. Have only used in very light current (neighborhood class-II) to test stability and roll in; however feel that might need to add a little something to keep knees spread. Not sure if it would be best to do this on inside of knees, or up on inside of thighs (any thoughts ?). If that's not enough, will chuck the knee hooks and build a small bulkhead.
Started outfitting on a section of 3" schedule 40 PVC pipe(super structure) just like a standard rail conversion. It's fitted into both walls, and glued into a channel cut into saddle. This really made whole saddle feel bomb proof top to bottom. Foot braces have been screwed together through pipe, and have no play at all. Rear of foot brace is (much) closer together, to lessen knee strain. Wasn't able to get feet to touch, but rear of Yakima's are down to 3" pipe.
Rear thwart will probably be used it to anchor (low) hip blocks off of eventually. Plus up under on each end (where u can't see) there is a 7/8" hole drilled thorough fiberglass to clip what-ever into.
Haven't cut saddle down very much yet (or sanded smooth) was 11"... is now 10". Stability has been way better than expected. Next will likely build up foam a little behind seated area, to help stay locked in once sure of exact balance point. Entry into is good and wet exit is almost like from a canoe. Believe it might be a comfortable steep creek setup, which was the intent of this project.