Well. If you are drilling the back glass and the hole is 1 1/2" I would put the center of the hole one inch below the rim. I would also reccomend to wait until you get the bulkheads in to drill it. What I did was place the nut part of the bulkhead against the glass. I then got a sharpie and marked the inside of the nut. This would insure that the bulkhead has room to seal on the glass. You'll see what I'm talking about when it gets there.



