Problem solved. Ended up getting a piece of 16ga steel from Home depot and cutting my own discs with a hole saw on a drill press. Pilot bit removed.
Had them Tig welded by a friend today. Weld looks well done, professional looking.
I'll paint over the affected area and that's as good as it gets. Can't imagine having any rust issues. Tank was in excellent condition to begin with.
Should increase the cars range to 650-700 highway depending on load.