To replace a door on a mobile home, unscrew the old door from the frame, pry it off, remove old putty, apply new putty along the flanges of a replacement door, fix the new door in place, and secure with screws and deadbolt locks. A drill with hex head bits, drill bits, screws and a screwdriver are handy in the project.
Unfasten the door from the hinges with a screwdriver, and remove the door from the frame, taking care not to mar the siding. Measure the height and width of the opening with a tape measure, and use the dimensions to purchase a replacement door from a mobile home supply store. If necessary, increase the size of the opening or cut the door accordingly to fit in the opening. If the door doesn't have pre-drilled holes for deadbolt locks, use a drill and appropriate drill bits to create the holes.
Scrape old caulking or putty off the frame. Lay a bead of caulk or putty tape along the edges of the replacement door, and strip off the backing of the tape if required. Insert the door onto the opening, check for square, and carefully drill screws to hold the door in place. Install the deadbolt locks, and test the installation.