Due to the extent of the repairs required, I would strongly recommend buying replacement chassis members rather than patching. Only replace one part at a time with the cars weight spread evenly. You should also have the bare doors hung so you can check for distortion as it's very easy to twist the car doing so much repairs. Good luck.
maybe use a metal bender to make new box sections to weld back in.......any are you can see when you have cut rotted parts out run a wire brush over it then rust reformer...then blast with paint...gives it a better chance in the future
I have had the exact same problems using a gasless welder, I ended up digging out my old gas fed welder & repairing it, Then luckily I found a very obliging gas bottle delivery driver who "donated" a pub size Co2 bottle to my cause, just a shame he couldn't donate a Co2/argon one!, maybe you can find a friendly pub landlord to oblige you with a Co2 bottle as those little Halfords type bottles don't last very long & expensive for what they are.
