Someone in the composites forum suggested that I put in my CF laminate as additional spars (vertically through the wing) in very thin slots. I guess I'm not sure where the
stresses will come.

Good point on the engine mount. Probably gave out for a couple of reasons - overstressed plastic, bolts used for location not just clamping (loaded in shear), torsional stresses on plastic (from mounting only two bolts).

So do you think using CF tape on the LE edge would prove less than useful as well?

Rather than building the mechanical mixer I'm just going to use a GWS V-Tail mixer which will give me electronic mixing with my 4-channel. I presume that I need only use two servos rather than three. One for elevator/aileron and the other for throttle?
I can understand how the mechanical mixing works (elevator servo moving aileron servo on tray) but I cannot see how I would need two servos for this using electronic mixing. I would just use a single servo that would respond to either elevator or aileron input, right?

cheers, /S.