One of the more uncomfortable aspects of being the rear-seater is the rear headrest; it's too far forward. Added to that, since the headrest is attached to the canopy, the rear-seater has no headrest with the canopy open, and needs to move out of the way to allow canopy opening and closing. Not terrible, but not optimal either.
Best bet would be to eliminate the two arrow stock shafts from the rear of the canopy. Put the rear headrest on the firewall; it would need to be thick...or, another fitted bag can go here (better packing efficiency!) I have a toiletries bag that would fit perfectly....
Simply eliminating the arrow shafts, though, lessens the torsional stiffness of the canopy. Maybe not enough to matter, but I wanted to add an arch over the backseater's head to compensate.
The arches (there are actually 3 of them) consist of 1/4" plywood, cut in an arch shape of 1/2" depth. The first arch is floxed to the very aft inside of the canopy edge; the second arch is floxed to it and is slightly larger, because its outside mates to the outer fiberglass skin, not the plexiglass. The third arch is similar, 1" further back.
Obviously, the foam in this area needs to be removed to allow installation of the arches.
Two BID layups went over these arches.
Then, the 1" channel between the third arch and the other two was filled with X-30 foam, and trimmed flat. This creates a foam channel section, after the next step.
Two more BID layups went over the arches and the foam channel.
This photo shows this step:
More X-30 foam was used to fair the arches smoothly into the remaining foam on the turtledeck.
The turtledeck was then glassed per plans (2 more plies BID).
It might be heavier than it needs to be, but it's torsionally quite.