I've actually taken Night Classes before, and they are pretty laid back as compared with classes during the day (At least in my experience). And while I don't work 40 hours a week, I do take 18 hours a semester while juggling other campus activities such a tutoring, class treasurer, etc. I do have respect for you though, that's a tough life.
But each time I think I'm too exhausted to keep going, you just gotta know you're building a better life for yourself one day, one step at a time. You have the rest of your life to party and have fun, etc.
Keep it up bro, you'll be fine, good luck,
~Jim