Many mobile home doors are actually smaller than a regular, standard home door. This means a store-bought replacement pre-hung door will not fit into the mobile home opening as is. The standard door must be cut down to size to be installed in the mobile home. This is one option when replacing your mobile home doors because standard-sized home doors are typically more readily available at home improvement stores. It takes skill with a saw and care in execution to tackle this project.
Pull out the old door's hinge pins with a pair of vise grips. Set the frame of the door on a pair of sawhorses. Pry the bottom portion of the pre-hung door off the frame with a pry bar.
Measure the door height with a tape measure and cut the new pre-hung door to the measurement with a circular saw. Subtract enough to account for the bottom threshold of the pre-hung door you removed.
Cut the door itself with a circular saw to the height of the door minus the width of the threshold and 1/4 inch to allow the door to swing easily. Slide the door seal on the bottom of the door after cutting it to the width of the door, if necessary.
Place the frame into the opening on the mobile home door frame. Level both sides with a carpenter's level and adjust as necessary by sliding shims under or along the sides of the frame. Tack the frame into place with finish nails and a hammer. Hang the door in the frame by lining up the hinges and tapping the hinge pins through them with a ballpeen hammer.