A few notes about you panel…

I’m not very crazy about applying glue to those miters, you see, end grain doesn’t glue well, and applying glue to fill the pores is only going to help in creating a mess…. and ask for lot’s of trouble….

Since you already have the miters and you don’t what to cut new pieces, I would do some floating tenons to glue the miters. You can just use four small squares of plywood and chisel out the mortise on each piece.

This way you’ll have face grain to apply the glue, and it will yield a cleaner joint. Email me if this is not clear to you.

Also, using this method, I would apply glue to all four corners and glue them all in one step. Then measure each diagonal and check if they measure the same. Adjust the angles until they do….

I would use small F clamps for this glue-up, but that is me, others will have other ideas…. But since your lid is so small you can also use a large rubber band. I guess that will do just fine. Put the rubber band around and check the diagonals and let the glue dry… Sounds easy. Good luck.

Take care,
Luis