I replaced the Attwood that was in my TC, it came out through the outside. Mine was a manual pilot. I upgraded to DSI ignition. I did have to install a switch, and run a 12-volt wire to the water heater. The DSI is great. I flip the switch about 30 minutes before I need hot water, or just leave it on. Before the DSI, I would be in the wind and rain trying to light it. Go inside the TC, wind would blow the pilot out, then I go back into the foul weather. I did not want the 120-volt option or 12-volt for heating the water. Just propane with the DSI ignition.
Due to size and shape, I doubt you can change from one brand to another. Each of the brands do have several models to choose from. The Attwood does not use an anode.