Dual 6V Battery Box

I'm upgrading my sons 5er from 2 12V batteries to 2 6V located in the front storage compartment. I'm looking for a reasonably priced and lighter box vs the heavy duty, heavy and high cost ($65+) ones. The box will need to be sealed and vented (a DIY project) since it's going in the storage compartment.

Anyone know where I can locate one? I've found single $10 6V boxes that look acceptable but would prefer a dual box.

Thanks