When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If your box is a sealed box, then yes seal the box up. 3/16 isnt too big, so i am guessing its not a port, so i would seal it. Did you buy this box used, if so maybe the previous owner had it mounted using that hole.