A cautionary tale and how to fix it if you are in trouble:
Forming the rudder (and the keel, really) shouldn't be challenging: Sand/saw a taper in a block of wood, glue to one side of cut plywood, then glue the other side of plywood. If the wood blocking is tapered on both sides, then the final shape should also taper on both sides. But that isn't what happens! At least for me. I've never seen anybody on a blog or on this forum have trouble with the rudder staying in alignment. Has that been a problem? In the manual it seems very easy.
See picture:
I think during gluing, the weight of the clamps and wood pushes the blocking "sideways" away from horizontal. Gravity makes one side of the board completely straight, and all the taper is forced into the other side of the wood (which is now "double" tapered, twice what the taper should be). What I should have done to avoid this issue is glue/nail the blocking together FIRST before attaching the plywood sides. That will force the blocking to be in the correct alignment with itself. Then, glue the sides together. Since the blocking is glued in the correct alignment, the sides will be forced together properly.
I don't have enough plywood to correct my problem (and it's not TERRIBLY bad), so what I'll do is mimic the correct taper by removing some material from the "front" of the rudder (facing the boat) to make both sides taper the same amount. Then I'll remove the "bump" from the 5-inch blocking by sanding through a layer or two of the plywood. Since it will be fiberglassed, I don't think it will affect strength too much. The end result will be a constant taper in the rudder from 1.5 inches (or whatever it is) to 0.75 inches.
I'm pretty bummed I messed up at first, but hope this tale can help somebody else not make the mistake.
(Since 0.75inches seems rather thick to end your taper on, I'm also going to glue an "extender" of pine to the end of the rudder, running from the top of the back of the rudder down to the baseplate. It will be flush at the rudder (0.75 inches) and quickly taper back over an inch or two to maybe a quarter of an inch. I also didn't see it in the plans, but I will round-over the front of the rudder and sides of the baseplate so I don't present a square shape to the water)