How to remove outer water heater door on 2007 Winnebago?

You shouldn't have to remove the hinge. Inspect the lower front and rear corners for a few screws holding the panel shut (instead of the latches all of the regular doors have). Removing those screws should allow the panel to hinge up. You will need to support it with a broomstick or something, however, since it won't have any gas cylinders supporting it.