I did not do a drop out box on the 36, I mounted it on the frame in the right fender. I used a universal unit that I got from speedway for about 30 bucks. Would be simple to fabricate though, use some angle to make a box that will fit the base of the battery, then weld a couple of runners to go up the side of the frame, then gusset it for strength, and finally some type of a hold down. I have been using this for 8 seasons of rod runs without a problem, but my car is full fendered and it is low so to remove the battery the car needs to be jacked up.