First up I will reply to 313 post .....The section I replaced was badly dented and had a few pin holes, in my opinion it was easier to do this than shag around filling rust holes and pulling out dents.
A hole was drilled in the frame to allow heat and hot air to escape while welding.
Lozza .... GI pipes are history. It's PVc or HDPE

Bazza ..... Lithgow looked like brass monkey country to me

and Yes The Girls enjoyed the Snow.