Water tanks, water heaters, stainless etc.
Talk to your local Plumbers. The frequently replace hot water tanks, and some are still OK, no pinholes rusted through.
If you can get some of these tanks, strip off the outer case, the insulation, and remove all plugs, drains, and the anode.
Rinse the tank well.
Then replace the anode (corrosion protection, and just a few $), and plumb the tank like you would for an under-body installation. Make sure there is a drain to empty the tank!
BTW, with your own water heater, if there is an anode, replace it at the halfway-point of the heater's warrantee date. In other words, if it's an 8-year warrantee, replace the anode at 4-5 years.
Drain/flush the tank once a year, regardless of it's age, this will blow out any iron or other metal flakes that can promote corrosion.
Do this for your house water heater, as well.
I know ONE guy has a water heater in his house, it's STELLITE, the same stuff jet engine nozzles are made of. The manufacture date? 1956!
He's gone through three burners in the damned thing, and it's still going strong. I am SO jealous!!!!!
Which also brings something to mind:
Stainless steel tanks are used in dairies, breweries, etc. Call around, maybe you can find one in a salvage yard, equipment auction, etc.
Put the word out with dealers and friends, maybe they can find you one in their travels.
The tool storage is nice, but where do I put the bed?