When I was young my first job was working at a chroming place, the problem you will have chroming a tank will weaken the metal and the welds, you could be opening a can of worms, some places might not go down that road and if they do it will be expensive and no garenteed that it will last and being a old tank could be even harder to do, but mine you I was 15 years old then and things might have changed, I only worked there for 1 year and I worked with the operator that pressed the button for the chrome tank, my job was to wash the parts as they came out of the chroming tank.
Ashley