Rust - where to look?

I am in the market to buy an M715. Where are the key places I should look for problematic rust? I realize there be surface rust that’s no big deal. Thanks everyone.

Behind the seats on cab floor, rocker panels inner/outer, hat channels on bottom of cab floor, bottom of doors, front fender side panels, lower front grill valence/apron, rear frame cross member, bed stake pockets and inner front wheel well.

Bad rust will be easy to spot on these trucks.

I will add a location that is kind of hidden.
Mine was rusted out pretty bad in the cowling, behind the top of the firewall, to the point that water would run down on your feet.
Major cause of that in my truck was from a huge, tightly packed mouse nest.
Stunk to high heaven trying to clean that out.