If, as you say, you have a minimum 0.024" steel or 0.032" aluminum bulkhead attached to the rear seat area and also to the shelf panel where the speakers used to be, then you can put anything you want to in the trunk, including pump(s). The idea is that if you were to stand the car up on its grille against the wall and fill the trunk with liquid, no liquids would enter the driver's compartment. Make absolutely certain that the bulkhead is liquid-proof. Have a buddy inside the car at night to observe while you shine a strong flashlight all around the trunk area. He should see no light.