The tubs for my new AP rack are getting delivered tomorrow!

Holes: how do you make them? I used a drill on my current tubs and they left sharp spots and sometimes cracked into the tub a little as I was drilling. They're pretty sloppy holes from the drill with a 3/8 in bit.

I hear people use soldering irons, like the 10 dollar one at Walmart. Doesn't that leave burnt black plastic goo around the edges of the holes? How do you avoid that?

I see some people who put 2 holes in the front and 2 holes in the back and call it a day. Others make elaborate arrays of holes across the whole side of the tub. What kind of humidity differential do you look for in maintaining that balance? 10% higher than outside? 20%?

Those of you who have nice clean-drilled/melted tubs... how do you do that?!