if you can get a leatherman mini it will fit in a altoids tin. and that will give you a full size set of pliers in a small tin.
i luv your altoids tin its like a mini tool box. its got a lot of capabilities in a very small package.
I make my little altoids crisis kits for hiking etc waterproof by wrapping the seam in insulation tape. The tape itself was a godsend when the sole of my boot came away on one walk.As for waterproofing a tin and using it regularly, I wouldn't have a clue mate - sorry. There are waterproof options like otter boxes, but I understand they're much bulkier