you could always put a wing spar in during the build.
and when you join the wing, dont just expoy the wing band, you leave a weak edge, take the expoy its self out about a inch past the band, a diamond band shape is even better to spread the loads.
personly i'd add a 1/16th ply spar after the wings are joined if i was worried, use a hackasw balda to cut a slot maybe 6" out into each side, 12" slot right on the thickest part of the wing, then fill the slot with PVA and slide some ply in. when its dry i trim the ply sticking out the top and bottom of the wing to lend it in.
i did this on a fast delta, a 160MPH crash didnt break that join.