I'm assembling a corrugated sheet metal fence and I have installed the posts and attached the pieces of shaped tube (rectangular cross section) horizontally and now I need to attach the metal sheets to the shaped tube. I'm now using a handheld drill with a regular drill bit for metal to drill the through holes in the tubes (I'll use screws with nuts later).
Drilling is a huge pain. First, the tube is only attached to the posts and so it bends when I press the drill onto it. Second, the drill bit will not dive into the metal unless I use a punch which is not a convenient option because I need to first put the sheet onto the tube and once I do that I'll have to punch through the sheet. Finally, even if I drill one wall of the tube the drill bit will then not dive into the other wall - it will be "running" for a while and the side surface of the drill bit will route the hole in the first wall. The result is really ugly and drilling takes a lot of time.
How do I drill through the shaped tube conveniently?