installing window A/C through stucco wal

hey all, I am in the process of installing a window mount A/C through a stucco wall. The question that I have is how do I best keep moisture from penetrating from the exterior opening. I am framing it so if I wanted to at a later time I could put a window in, but for now I want zero clearance between the A/C unit and the hole cut in the stucco.