Corrosion at rockers, floors and frame rails is the primary NA inspection point, with salt-belt cars far worse than west/south-coast examples; the hollow frame rails are really 'support' rails prone to smushing from bad jacking, and cowl drains dump leaf debris and moisture behind the front fenders where rust starts.
Rust: rockers, floors, frame rails and cowl-fed fenders
Mazda MX-5 Miata (NA) · mechanical