4mm ply was used because it was just what was needed to meet all the objectives of weight, strength and stiffness given the selected glass laminate.
So I take it there's a glass layup over the ply as well as just taping the joins?
I believe the timber T4.9s are not fully glassed over which would make a fair weight difference.
I'd be interested in seeing you're construction pics Phill maybe a future posting for all to enjoy!
Cheers Phil
