I've got a sub box in the trunk that slides around and I'm planning to bolt it down with some mounting brackets. My concern is, how can I make sure that I dont puncture the brake line or the gas pipe? I'm driving a 94 Camry

We can't really tell you exactly where you can drill to install the brackets without being there. All that I can really tell you is to jack the rear of the car up with a floor jack from the crossmember and slide under to see where everything is located in the trunk. Find out where you're wanting to put the brackets, and figure out where all of your lines are.