Quoting Sierra94:" not really. we're doing just fine. I mean we don't have thousands of dollars in savings, but we're not lacking for anything."
I think you're somewhat overreacting. You guys should probably stop being dicks to each other when you're tired and so on. It's something that's going to happen regardless of a night shift job. No, I'm not saying you ARE a dick, just an expression.
What if something happened to SO? Do you have enough saved to live on while he's recovering? Do you have enough saved for another vehicle if yours dies? It's always good to have a little something extra set back. He doesn't have to work the second job forever, but setting up a nest egg is a good idea, IMO.