The opening for the old water heater was "Huge."
It was in need of a big "Patch" to plug the irregular sized opening. A smaller opening will be created later for a modern water heater. It will "look" modern and will not protrude three inches from the surface like the old one.
I cut out a patch from the same composition aluminum as the body to cover the hole.
I drilling and spaced rivet holes evenly which took patience.
Buck rivets were used here since the back side is exposed and accessible for a bucking bar.
A horizontal brace about five inches from the top was also re-installed on the back side to add strength. (See the secondary rivet line.)
The old water heater was so large that this brace was "cut out" to make room for the install.
The finished patch looked great and blended right into the body.
When I install a new water heater here it will require a much smaller surface cut out.