[hiccup]

Just offering my two cents to help you think through the pros/cons of different approaches. That does not look like an easy job. I agree gaining as much access to the top of the tank makes sense. I would want to hear the yard's plan for creating the cutout and hatch in the floor. I would expect the best way would be to create a template and cut it out with a router. If that isn't done correctly it will never look right.

But before that I would want a complete inspection of the inside of the tank using cameras. If the tank has a few small pits, and they will be accessible with the access you will create, your plan might be a good one. However, if the entire bottom and/or sides are pitting then I would not expect that idea to work well. In that case I would look into having a bladder made. I would try reaching out to fuel bladder manufacturers to see if they have any options. Best of luck and keep us posted.