One easy way to vent modern batteries is to use the small vent ports on many sealed batteries. GM puts some of theirs under the rear seat. Many including BMW does not use a sealed box, just vent tubes.
Also one thing I did Iearn the hard way is make sure your negative cable is at least 1 to 2 sizes smaller than the positive. Event the factory does this. When a worst case scenario goes wrong & the positive cable gets grounded through a short at the firewall or starter when you crank the engine, you want the short ground in the trunk to burn not the 20 foot long positive wire running the length of the car.
Here is picture of a vent tube and therre are several styles. GM's are oval.
I relocated my battery to the trunk, put it in a NHRA approved box and discovered that the battery is puking acid in the box and it's dripping out around the hold down bolts. The car has a Powermaster GM one wire alternator and according to them is functioning properly. Now I need to rethink my battery selection.
