The white All Battery boxes are not sealed. For my son's fiver we sealed the dual 6V box which is located in a storage locker.
1. Added a high and low vent connected to the outside.
2. Glued a plastic cover for the U shaped battery cables. Then drilled a hole for a tight fitting rubber grommet to seal the cables.
3. Added a foam strip to seal on the inside top cover to seal it.
4. Installed a hold down strap.
The results were a vented sealed battery box that fully protects the electrical terminals from his items to be stored. A DIY project with no wasted space for battery box handles etc.