tph1: Elmers does make a Polyurethane based glue under the ProBond label, but they also make a rosin glue under that neame too. Be sure the bottle say polyurethane. Another brand is Gorilla Glue. I've used both and can't tell a whole lot of diff between the two other than the Gorilla glue is more expensive.

I've put five planes together using the poly... everything from 35% Cardens to 2M pattern ships. I pretty much use the method described by Toymaker, and would like to add the following.

I've never had a problem with glued skins floating when attaching LE or tips. I use the poly on these items. I then use generous amounts of masking tape to hold the LE/tips in place. Basically, I run a strip of tape then move over the same width as the tape and put on another piece, etc.

FYI: You cannot vacuum bag the wings. Poly needs water to cure.

Instead, use weights as Toymaker described to prevent the wing skins from floating off the cores. I typically run about 1 lbs per square inch. This can be a LOT of weight, like 500 lbs for one wing panel. It is critical that your building surface remains true under this weight. I typically set the cores/shucks on my reienforced table, place a 3/4" particle board on top, and then load up sand bags to the desired weight.

Cheers.