Mobile homes are a special breed of construction.......ther are unique products and situations that only occur with them........
The door(metal?) and the metal frame sometimes are attached with a long hinge(piano) or special riveted hinges that make the unit a single piece......no way to replace just the door alone.......Other doors may be attached with screws and allow the door to be replaced separately........
But your FRAME may be leaking.......If the door is in good condition otherwise....not bent/broken/etc......You may be able to remove ALL the many screws from the exterior flange and remove the existing door and frame .......clean up the opening and any framing problems you find......and reinstall the existing door back into the opening with a quality silicone caulk as a sealant........
You're welcome to e-mail me direct for additional response......click [name] above........good luck doug