Thanks again for all the feedback, folks. I received the replacement tabs skins from Van's and took another crack at it this morning:
Certainly came out a lot better! I used the steel bar method both times, but this time I went through great pains to get everything locked down with carpet tape and took my time with the bend, using a rubber mallet and a block of wood. I ordered two trim tabs, so I've got one more crack at it (might as well see if I can do even better), but I'm feeling pretty good about this one being usable no matter how things go the second time around.