You will get more useful feedback if you post what brand it is. There is plenty of info online about modifying cheap offset smokers, and most of the mods are inexpensive.
As for the firebox door, I've never seen one mounted "upside down" before. The manufacturer should fix it if it's a defect. If not or if it's homemade, just keep the existing air intake closed and put a couple of cheap ball valves on the bottom of the door. Don't put a lot of money into it.
A bunch of Webers