Been working on this for a few weeks and came across trying to figure out how to tie the rudders together on the booms...
The last few pics are the tail section and I did a mock up to try and work it out...
That entire forum thread is long and not really worth reading. I had issues with my first one but I don't fully remember what those issues were. Other than I made the plane big with a little motor. I think the only real issue was it being underpowered. Oh, and i cut into the wings to mount the booms, horrible idea. You are right to mold the booms around the wings.
I put bamboo skewers into the booms to strengthen them and the plane did take a lot of abuse.
For your twin rudders, what I did was with my first design I only used one of the rudders and for my second one I had no rudder. But you could mount control horns at the very top and end of the rudders and connect those two with a bamboo skewer with paper clips at the end. I don't know if that makes sense. But you'd be using a stiff rod to connect the two rudders and the control horns act as pivot points. As long as the two control horns are mounting at the same location on each rudder, then it doesn't matter where you put them.