There's a large galvanizing company call AZZ nearby me. I've sent some catwalks (outside for signs) to them as well as gangways for our machines. They did most of the cell tower sections around here back in the day. And for sure, you want to drill holes not only to allow the zinc to go out, but to allow it to coat the inside evenly for outside applications. If you leave the tubes sealed, at that temperature you can get bloating and other deformities plus, your tube can rust from the inside out if it's out in the weather.