I use a SmartStore 31 as my dry box. The lid has got good locks on the short side but tends to bulge on the long side.

This clip fits on the long sides, adding extra sealing of the lid. Combine with a weather strip in the lid for extra air tightness.

Print as many as you need, I use three on each side.

Print in PETG, ABS or anything else with a little bit of flex.