I wanted to find a way to put a lock on the box and found this on ebay for a few bucks:

 

http://oldsargesdropzone.com/product.php?item=1737

 

I probably could have just gone to home depot and get stuff, but it was an impulse buy so whatever.. anyway, just works on a 50 cal ammo can, drill a 7/16" hole and attach the hardware.. takes 5 minutes:

 

 

 

Not sure if you can see it well, but you can put a lock through that hole. For 30 cal cans or other sizes, I'll have to do something like this:

 

 

Anyway, figured I'd share.

I bought that same lock set up from eBay except i welded mine.

Thanks for that Old Sarges link. Lotta neat stuff