Running a screw into the edge of plywood splits the plys and has poor structural properties. The Kreg style pocket is much, much stronger. Exterior grade construction adhesive will really beef up the joint but can make things very slippery when trying to make up a corner. A temporary cleat can align the joint while you drive the pocket screws and then removed. I would look for Stainless Steel screws with a square drive head. Sheet rock screws are very brittle and rust very quickly. Even in 'dry' locations, wood transmits moisture.
