I disagree with the vise recommendation. I have a machine shop for building rifles, and access to anything I don't have- so I could choose pretty much any method including a mill w/ DRO. The
tanks I've drilled, I still opted to drill by hand -
tank in one hand and cordless drill in the other.
The material you are drilling is soft, thin, and the holes are small. If you try to set this up in a vise, and you are off by even just a little bit, you run the risk of getting off-center and breaking your drill bit.
Because the hole is so small and the material is so thin, you can do a better job of "floating" the drill to center. The last couple I did, I left the drill standing on its battery and pulled the trigger with on hand, and just guided the tank onto the spinning drill bit. Took all of three seconds to open the hole up. It would've taken me long to grab it in a vise, let alone center it up.