There are any number of videos on You Tube on removing dents
from (motorcycle) gas tanks without cutting them open.
While cutting open a tank can really speed up the process with
time and patience I have learned how to removed most issues from
a tank. After getting a tank as straight as possible using air (above)
I move to the method in the video description box. The process is
ongoing as I’m always trying different things to use as tools but its
really nothing more than everyday automotive bodywork.
https://youtu.be/U5NActQ9LOw?si=M7GCMUck77dCvi3K
Tubs.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.