Rob,
it looks good. Hard to tell about seams/reinforcement from the picture, but I am looking forward to hear how it turns out.
Why did you go for a solid trampoline instead of mesh? I personally prefer quite tight mesh trampolines. I find them easier to move about on, not as slippery, water doesnt pool up and it lets some wind trough it.
Regarding tightening the trampoline drumskin tight to stiffen the boat.. There has been some discussion and testing on this in the Tornado class. Unless your trampoline is bias cut, tightening it hard enough to rip tracks/fittings out of the hulls will not stiffen the boat significantly. A bias cut trampoline will take some of the diagonal tension and help stiffening the beams if they are underdimensioned.