There is a bin at Lowes...says Project Boards....mostly thin boards of Pine, Poplar and Oak....that you might want to check on.
A combo or plough plane can be set up to plough a third groove around the insides of a box ( mark that location on the outsides) and then glue the box together. After the glue has set, and cured...use the plough plane to cut a groove around the outside of the box...right below the inside groove....IF they line up just right...
front view.jpg
A seal of sorts is made...lid has a lip, that covers the inside rebate....
lid open.jpg
Like this Poplar box made to hold a Stanley #45 in.