I once helped renovate an older modular home. The older ones are built in a very similar fasion as mobiles. Each company builds them differntly, but usually the ceiling joists are made of wood. Even if they are made of metal, you should be able to drive a multi-purpose screw into it. The only thing that Steve told you that I would dissagree with is your drywall. I personally wouldn't use anything less than 1/2" drywall on a ceiling. 1/4 and 3/8 don't have the integrity to maintain a flat surface on a ceiling. Gravity takes a toll over time.
I would also invest in a drywall jack. You can usually rent one and they make doing a ceiling so much easier, and they're very simple to operate. You still need to people, though.