Thanks everyone! I was taught that drilling stitch holes is a no-no and I don't like the way the slanted stitches look, so I'm strictly an awl guy. Think drill press that doesn't spin with an awl in the chuck.
I layed out the holes and punched them in the sides first. The center welt piece goes the whole length so that was next. I used the sides as a guide and punched the holes in each welt piece before assembly.
To assemble, I glued them in place one at a time. I had a needle in every third hole in the side as a guide. The the other side was last. I didn't realize it, or do it intentionally but my son noticed the top welt resembles wood grain, so I got that as a bonus.