I use this method too.

Using both sorgum and the Scotch 77 product, I've had delamination of the skin from the core.

A few tips.

1) Sand the skins after edge joining them (the side to be adhered). Any irregularities will prevent an intimate bonding. Also cut the skins to allow a 1/4 inch edge all the way around.
2) vacuum clean both the skins and the foam... many times!
3) I apply the adhesive to both the skins and the cores.
4) Make sure you get the Z-Poxy finishing resin. (Part#Pt-40) www.franktiano.com/ZapFrameset-3.htm
5) By using this product, the foam cores become "safe" to use polyester resin on the wing exteriors.
6) Make sure the resin is room temp. Escalating the resin to 80 degrees might shorten working time too much.
7) Balsa and obechi ply can be adhered equally well.
8) By using the resin that hardens, it reduces flexibility in the finished wings.
9) Using high temp films to cover the wings can be frustrating. Stick with moderate to low temp films.

Definitely set the cores in the shucks onto as flat a surface as possible. Top this with a single piece of plywood and equally distribute a hundred pounds across the ply.