I've built four strippers to date and just finished, well, mostly finished, a retrofit of the first one which I kept for myself (it's a sentimental first-love thing). That said the second through fourth I installed 1/4 inch solid-core plywood (not marine grade). The rear bulkhead slants aft to join with the forward edge of the rear-most inside edge of the coaming. In other words, a reclined seat back. The forward bulkheads all are 1/4 inch ply angled slightly forward at 18 degrees which seems to be the average of everyone's natural angle of their foot. The fit of forward and rear bulkheads to the hull and under-deck was very time consuming to make as tight and perfect a fit without gaps.

Installing the bulkheads, if your interested in how the 2-4 yaks bulkheads were installed....
I lightly glassed the inside faces of forward and rear bulkheads with 3 ounce triaxial glass just for waterproofing and some strength. The bulkheads were glassed into the hull (deck not attached yet but a joined and taped deck and hull was used to make the bulkheads) using 6 inch wide 6 ounce glass tape cut so that the edges extended up up the sides about 3 inches. Cured, sanded smooth and washed with hot water and scrubbed, and rinsed for any blush, dried and then I cut 6 ounce glass so that it would cover the bulkhead and a bit of the hull, and draped it onto the rear-side of the rear bulkhead and the inside face of the front bulkhead, wet it out and used a pint brush to dab it down. After curing, I did the same but tilted the hull the opposite way and did the opposite faces of the bulkheads. Joining deck and hull was a little easier then the first yak. After joining, I used 6 ounce glass tape to glass in the bulkheads to the deck. I should also mention that I set in stainless steel T-nuts for mounting the Bosworth Guzzler 450 S foot pumps. The idea was that the front bulkheads function as both footrests and a foot pump location. Adding or removing layers of 1 inch thick closed cell foam adjusts the length of the paddler and fine tunes the fit. The foam was cut from those foam 4-packs at Home Deport for $20).

Retro-fitting the first yak...
banging out the 1/8 inch bulkheads was hard and time-consuming. I also banged out the hip braces which had delaminated and proven to be too weak over time. Sage of this KBBB suggested filling up the cockpit with as much foam padding to lower the cockpit volume and make for a comfy fit. Retrofitting the bulkheads with 1/4 inch was both easier and much harder, I only just finished the front bulkhead just before the first of two sail trips. I have a back issue and must recline back to paddle long distances daily, so the POS Bomber backband was tossed into the trash where it belonged (cheap buckles, cheap construction, rotted stiching and real asses at Bomber Gear) and cut and shaped a peice of stiff minicell foam to fit tightly under the coaming and against the rear bulkhead, shaped to grip my back like a bucket seat, and jammed into place. Since this was my first yak design, there's a need for a rudder in certain conditions. I'm still constructing the combo footrest and rudder pedals out of foam and extruded PVC board.

Hope this helps...getting some ideas, experiences and approaches to the problem.