OK, thanks for the tip @JadeEyePanda. It took a little while, but here's the new UV map: Attachment not found. And the tank now looks like this: Attachment not found.
@BringMeASunkist The main resolution issue I'm having is that I can't put enough detail into the tank (i.e. a 1px thick scratch is too thick). My UV map is long and thin, so I chose a map that I could get the most detail out of (without any wasted space). @JadeEyePanda OK, maybe my UV map is screwed up. Here's my map (just…