Should I just use more/thicker coats?
Holy smokes, don't do thinker coats. Here are some important things to remember:
-Don't skip the primer. Primer sticks to raw wood better, dries faster, and is a better base for your final paint. (if you already skipped the primer, don't worry, there's nothing you can do now and it's not like the cab is going to fall apart)
-Make sure each coat is dry before applying the next coat or it will take forever to dry.
-Using many thin coats is the best approach. They dry faster, it is easier to avoid runs, etc.
-In general Gloss finishes are stronger than satin finishes.
Those are the basics. Search around, others have posted detailed tips based on experience. It seems like Frosty went into detail based on experience from his previous cab, but I'm not positive.