I can tell you what to seal the connections to the box with. Any Marine store will sell you a tube of 5200. Some hardware stores may even have it.
You will need to sand off the slick finish on your container, unless you use glass
Then wipe it clean with Alcohol or brake cleaner.
Apply the 5200 around both sides of the container, and install the fitting. Tighten snugly, but, don't try to wring out the last little bit of 5200. Wipe off everything in sight with Mineral Spirits.
Trust me. You will have this stuff in places you never thought you went to, after using it.
Once dried, 24 hours or so, you have a strong, flexible connection, that CAN be removed with a hardback razor blade, IF you are careful.
This stuff is used to seal leaks on boats while the boat is IN the fresh or salt water. IT WORKS.
DO NOT get the fast dry. 5200 in White or Black, whatever fits yer color scheme.
ALSO, have y'all ever seen Battery Promo boxes
Y'all know what I'm talkin about. It's simply a Lead acid Battery box, used in Displays. Comes with compartments and the top comes off. Posts are molded with the top. Just drill and mount the leads.
They come snapped together, or partly glued. I have one, somewhere in Fl, IF my Son hasn't cleaned out the warehouse and trashed it
Call or stop by your local battery shop, and see if they can getcha one
Battery cases will hold some pressure, especially with brackets and 5200.