The width of my bulkhead is a bit wider than the Plan's dimension - mine is ~18". I used a carpenter's contouring tool to determine the profile of the fuselage where the bulkhead meets. Then I transferred the profile to a 3/8" PVC foam. After minor shaping and sanding, the bulkhead fits against the fuselage sides nicely. Note the profile of the foam?
According to the Plan, the rear thigh support follows the same curvature as the front. However, if you check the dimension closely, you'll find that the ribs (for the thigh support) are shorter in the rear than the front. Therefore, the thigh support curvature is steeper for the rear. In addition, the Plan does not call out any supporting ribs for the rear seats. According to the archives, no one seems to know why either.
I made a set of 3" wide hinges and embedded half of the hinges in the top of the foam. I also drilled a couple of 3/8" diameter holes through the hinges for flox anchor.
To be more precise with the curvature, I decided to make a set of ribs to help shape the rear thigh curvature. This time the thigh supports rest on top of the bulkhead (instead of level to the IP edge in the front). Once the ribs were made, I hot glued them in place such that I could make the thigh supports to the appropriate curvature. I lanced the thigh support foam per Plan. I added an extra lance at about 1/2" from the front most edge. I also rounded the front most edge for a smoother transition.
I glassed both sides of the bulkhead with 1 ply BID. I used a laser to determine the slot location on the armrest where the bulkhead protrudes through (as shown). With the slot cut, I hot glued them in place first, such that I could establish the hinge positions for the back seat.
Here's a picture of the completed thigh support. I have yet to glass the second half of the hinge to the fuselage bottom.
The seat backs are pretty straight forward - a 12" x 18" flat piece. Again, I embedded the hinges in the foam with flox and glassed as before. I hot-glued a 3" board between the two seat backs to keep them straight and parallel to each other. Then I lined them up in position per plan and floxed the hinges in place with 4 layers of BID.
I floxed the hinges for the rear seat and peel-plied the hinge sets at the same time.