Re: Old dog learns new trick...Welding!
I'm sure Dan knows this and will pass it on but, when you start to 'connect the dots, the tack welds, you'll want to start on the weld and overlap each one just a little. Alternate from side to side on the tank to reduce the possibility of warping the sheetmetal.
Good luck. Keep those photos coming.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"