Stanley your correct its a lot easier to replace than patch, I agree it's a pain to take the tank out when I did mine the tank was full. but a local garage gave me a new empty 200ltr steel drum, so I managed to save 95% of a full tank of fuel, the removal I did in 3 bits rear cross member them the rear side member and a final measure a cut to fit and weld the new section in, all done in 3-4 day at the tender age of 70, plus new rear brake pipes, as for welding gas I stopped using BOC, a I had to pay cylinder rental every year, I now use Hobby weld. 3000psi cylinder with it own regulator a onetime fee for the cylinder no annual fee, with a refund of 90% if you want to return the cylinder
there are some good repair chassis out there, I do take on welding jobs so any one close only need to contact me even if all the need is look over and advice on the best way to resolve a problem,