Venting trunk mount battery?
Two tips.
1) The optima is by far the cheapest battery you will ever buy, if you consider it on a cost per year. Mine is pushing 15 years and still going strong. I mighta paid $130 or $140 for it. That comes to just about $10/year. It comes with top and side posts, and,as its a group24 battery, it will fit nearly any car.
2)Its sealed already. Spiral-cell technology! Just get it.
Just make sure,for safety sake, to bolt that beast to the frame with serious bolts and crossbars. At 60 mph, if that thing comes loose, it will seem to weigh in the neighborhood of 360 times its normal weight.
It stops for nothing!