Cncottrill-
You may be able to have a welder repair your Atwood's tank.
I would buy a new Suburban SAW6D, SAW6DE or SAW6DEL, as appropriate (link
here). I'd rather not worry about a repaired tank's integrity.
Dometic bought out Atwood's water heater line a few years ago, and discontinued it. You no longer can buy a "new" Atwood unit, or a replacement tank.
Suburban, who already made their own line of RV water heaters, saw an opportunity in all those orphaned Atwood 6-gallon heater owners. They designed the SAW6D/DE/DEL as a "direct" replacement for the Atwood.
Now, I haven't had to replace an Atwood with a SAW6D/DE/DEL, but the promise you'll have to change nothing (or little) on your coach is there.
Current pricing looks to be $400 to $500 for the SAW6D and $500 to $550 for the SAW6DEL. Make sure you buy the model, and any other parts "sold separately," that meets your needs.
If you go with the Suburban you'll need to use an anode rod in the drain opening, which is standard for Suburban heaters but not for the Atwoods.
As for the Atwood 10-gallon heater orphans, well...