B pillar rust

[Lesliehedley]

I'm going to overhaul the B posts on my wedge over the winter. I've already had a look at them and base which usually rusts to nothing is still fairly solid, but there is a layer of rust which has lifted off the top surface. Does anyone know how thick the base should be on these? I'd like to know they are still strong enough since they take the seat belt mounting points. TIA