After framing up the tail surfaces, I laminated the horizontal stabilizer with 1/32" plywood, top and bottom. This added a bit of weight, but it sure strengthened the structure, and that was needed. It also reinforces the tabs on the ends where the vertical stabilizers fit. I was a bit worried about the strength of that joint, but I think its good now.

I thought I had a simple control mechanism worked out for the twin rudders, but couldn't seem to get the geometry right, so I had to make it complicated. Three bellcranks later, I got it all worked out. It's a bit Rube Goldberg-ish, but with a bit of Loctite on all the screw, it should hold up well.