Sorry for the threadjack, but these horror stories are only intended to boost your morale
I worked on an old Alfa Romeo (Junior GT IIRC) trying to patch the engine mount chassis rails, and try as I might (using gas weld in those days) I couldn't get flow on the weld. It turned out that the chassis boxes were foam filled, a trick Alpha used to get away with using thinner steel... to stop the boxes collapsing under load.
I think it was all to do with collapsible zones in those days, trying to make bad driving safer for the occupants.