There are a lot of different glues that work, and Goop is a really good one! I like the CA because it's almost instant and I can build a complete 4 channel sport plane in 3 hours, or a combat plane in two. As for the flutes, when using 2 mm coroplast, going spanwise flutes is almost impossible to get a smooth airfoil without the coro "breaking" over unless some sort of internal support is used. When using 4 mm coro, spanwise flutes work great on the triple facet airfoil used on the SNS and Devastator. We also use 4 mm spanflutes on the bottom of the RNAF style wings with 2 mm coro being used chordwise flutted on the wing top.