Use fiberboard or textured gypsum wallboard. The wallboard is more widely available. (Be sure to fix the problem that caused the damaged panel before replacing it.)
Here are some tips:
* The panels installed in the factory are four feet wide and run the width of your manufactured home. You're not likely to find a panel that long, and if you did, it would be hard to handle. If the whole panel is ruined, replace it with two eight-foot panels cut to fit. Or, cut away the damaged area and add a new piece. It's a good idea to find someone to assist you because these panels are difficult to install alone.
* Matching the texture and thickness of your panel is more important than matching the color. You can always paint the ceiling after you've installed the new panel.
* You will also need to match the battens-the strips that cover the grooves between the panels.
* If the damage was caused by water, the insulation must be dried out or replaced. While you have the ceiling open, you might want to add more insulation. If there is no vapor barrier between the insulation and the ceiling, add one. A vapor barrier protects against condensation moisture.
* The ends of ceiling panels are installed between the sidewalls and the roof. You don't need to dig these ends out. Slice the ceiling panels at the wall edge. To support the new panel and cover the edge, add 1 x 2 molding strips that have been stained or painted.
Gypsum wall board is pretty widely available at lumber, materials, and large hardware stores. Hope this was helpful!