I would recommend an Aliphatic woodworking adhesive. This is a type of adhesive rather than a trade name. It has a number of advantages over over ordinary types of water-proof woodworking adhesive. Apart from being waterproof, it has a more rapid setting time, is sandable when dry and tends not to leave a stain around the joint.
There are number of manufacturers/suppliers. Here is a link to a supplier that I use for a number of modeling adhesives. They supply by mail order but also attend many of the modeling shows.