They have those at autozone for $12, I had one too. Its not sealed, and mine cracked cause my batt is too big lol

I choose againist mounting the battery in the bin location because its curved there so unless you want to fabricate some kind of mounting plate for it first. I went with mine in the rear of the car by the strut towers on the passanger side. Theres a flat area that it mounts up too well. My car has exactly 50/50 to the pound f/r bias and cross weighs and left to right is 50.5/49.5 with driver and 11 gallons of fuel so it worked for me.

Alot of you are saying plastic, but if the purpose of the box is to pass NHRA regs, it must be 1/8" steel too.
Food for thought.