Apply a sealant: Apply a waterproof sealant around the edges of the box to prevent water from seeping in. Silicone sealant or a marine-grade sealant are good options.
Install hardware and components: Once the box is sealed, you can install hardware such as latches, hinges, handles, and gaskets. You can also add foam padding or other protective materials to cushion your electronics.
Test the box: Before using the box, make sure to test it for waterproofness. You can submerge the box in water and check for any leaks or water intrusion.
Making an aluminum waterproof box electrical requires some technical skill and equipment, so it may be best to hire a professional or purchase a pre-made box if you're not experienced in metalworking.