Turn off the electricity to the existing ceiling light at the mobile home's fuse box. Remove the screws holding the existing fixture to the electrical box. Disconnect the wires holding it there. Pull the light free.
Pull on the exposed electrical box. If it moves at all, take it out of the ceiling by removing the mounting screws holding it there. Insert an electrical box support bar between the two ceiling joists, slipping the bar up into the hole left by the box and expanding it between the joists according to the instructions that came with the bar. Reinstall the electrical box to the bar.
Attach the mounting bracket that came with the fan to the electrical box using the screws that came with it. Attach the bare copper ground wire from the electrical box to the green ground screw on the bracket. Tighten the screw.
Assemble the fan on the floor, following the manufacturer's instructions. Don't mount the fan blades yet.
Bring the fan assembly up the ladder, getting it close enough to the electrical box to connect the wires. Connect the white wire from the box to the white wire from the fan, and put a wire cap over all three of them together.
Raise the fan to the ceiling, pushing the wire connections up into the ceiling box. Attach the fan housing to the mounting bracket using provided screws. Restore the power and test the light and fan motor. If they work correctly, attach the fan blades according to the instructions.