If you don't already have a dado set, they are expensive and I wouldn't buy one just for that. They can be cut with a table saw that has a titing arbor but that process is tricky and can be dangerous if you don't do it just right.
I would recommend just nailing and gluing a cleat onto the outside of the boxes for a handle. Take a piece of scrap wood that is two inches wide and the same length of the short side of your boxes, rip it in the middle with your saw blade on about a 15 degree tilt. That sould yield two cleats that you can nail on so that they are under-cut for better grip when you lift tie boxes.
I would recommend just nailing and gluing a cleat onto the outside of the boxes for a handle. Take a piece of scrap wood that is two inches wide and the same length of the short side of your boxes, rip it in the middle with your saw blade on about a 15 degree tilt. That sould yield two cleats that you can nail on so that they are under-cut for better grip when you lift tie boxes.
