I’ve experimented with different ways to hold a lid down, and I’ve found that 1/8″ square magnets are the easiest to install and give the best results.
You’ll need a little tube of cyanoacrylate glue – commonly known as Super Glue, Krazy Glue, Instant Glue, etc. I find that the brush-on version is the easiest to use: http://amzn.com/B000GATVQI
These neodymium magnets are strong enough to hold the lid on your insert, even if the entire box is flipped upside-down. If you end up needing more, you can get them from K&J Magnetics: http://www.kjmagnetics.com/proddetail.asp?prod=B222
First, find a metal surface to organize your magnets. Pull them off into sets of 2. (I often send a few extra magnets, so don’t worry if you don’t use them all.)
Locate the little cutouts on your design where the magnets will be inserted. Brush some super glue into the cutout, then place a pair of magnets into the cutout. Avoid gluing your insert to your game box, and also avoid getting glue onto the upper magnet. I suggest you install the magnets in pairs so they’re easier to handle, and also to guarantee you get the magnetic poles facing the same direction. (Nothing’s worse than getting your magnets permanently installed only to find that they repel each other.)
That glue will set in about a minute, but I recommend you give it 10-15 minutes to dry. Test that the magnets come apart, make sure you didn’t glue them together by accident.
Now, leave all the magnets in place, and set the lid on top of the insert, so that the magnets fit into the cutouts on the lid. Brush some super glue on the top of each magnet – again, being careful not to glue the insert to the box, and not using so much glue that the magnets get glued together. Give this another 10-15 minutes to dry.
If everything worked correctly, the magnets should be firmly glued in place – the wood will break before the magnets come loose. If any of the magnets aren’t secure, just repeat this process, and be patient.
Once everything is holding well, you can remove the lid and optionally apply more super glue around each magnet to make sure they’re secure.