Wayne's 1972 V8 rust

These areas rot from the inside out. Looks to me like something to be addressed very quickly before it becomes much more serious .

Yep, typical. The deal is that behind that fender in that area is the front of the outer rocker box section. Alot of loads go through that area, and it usually is rusted if the fender is. Wet debris gets between the fender and rocker in that area and then it's fed a supply of rain and wash water from the cowl drain.