Recently I found this British guy jademuttley who has what I think is a great method or procedure for repairing rust and he has done many videos sharing his expertise.
His genius is to break down the restoration into manageable sections; and modding or fabbing each piece of repair sheet metal by hand much smaller than I would have thought optimum before seeing his work.
Obviously he is an absolute master so he makes each step look super easy. but his results are hard to argue with.
I'll try to post a link but probably safer to just navigate to youtube and type in "jademuttley" (his channel)..
Here is an example from the series where he rebuilds what would have looked to me like a hopeless wreck hardly worth scrapping into a gorgeous car..
Here is a title:
Triumph Vitesse Restoration Part 3 HOW TO HD 720p
and a link:
https://www.youtube.com/watch?v=q1PAD5mfTxI