[folivier]

There is a guy on the Foretravel forum who has successfully replaced the copper tubing around the tank. Looked like a pretty big job but not impossible. His issue was the copper tubing leaking but it would give you access to the tank to either repair or replace it. You may need to be a member to see this: https://www.foreforums.com/index.php?topic=28387.0
I think the only difference between his aqua hot and yours is Newell uses 2 electric elements.