RE: Sig Mayhem 3D ARF
I don't think there will be an isue with the wing center section. I've flown my Sig 300 for a couple of years now and it does'nt call for it either and I put a big gasser on it. Just use plenty of epoxy. The plywood wing joiner should be very sufficient as long as you get it glued in right. I mounted my Webra 1.20 on it's side and it looks OK.
Steve