Can't make the Action Packer waterproof but you can make it more water/dust resistant. You'll still get seepage from the latch/handle holes.
- Buy some 1/2" wide adhesive backed medium density foam. (available at various hardware store chains)
- Use sand paper and rough up the groove on the lid.
- Clean the surface thoroughly.
- Adhere the foam, taking care to make cuts where necessary to round the curves.
If you want to go crazy, you can remove the latches. (you'll get the idea once you take the latches apart)
- Silicon this retainer to the body.
- Add a thin nylon washer here.
This has kept my items fairly dry for 5 yrs through 6 rain storms, and 2 white out conditions. With only a few drops of water making it into the containers. The key is not to ratchet down the Action Packer so tight and end up deforming the lid/container.