We have moved away from the issue. It's the inside floor of a truck that, after all these years, is not rusted out. Just rusty. Needs wire wheeled, converted and painted with spray cans. Some of the comments and suggestions are for outside of the vehicle or frame and hard parts. Most info here is too much work and not necessary for this specific question. I'm surprised no one has said powder coat or remove the floor and then junk the truck.
Sanding will not get into the floor pan joints or the stiffening dimples very well and may thin good metal while trying. In this specific question, wire wheel is the answer. A knotted wheel may be too aggressive, The crimp type may be better in this case. The modern converters/encapsulators specifically say you don't need shinny metal. They react to the rust as part of the gig.
This is a mental issue. Us old school guys have a hard time trusting this science. We are used to getting all the rust off down to shinny. Like doing an expensive paint job on a truck body. This ain't that and the conversion/encapsulation chemistry/science is proven. I don't see any flaking or sheets coming off but I only have one picture to look at. It looks like floors I've had a few dozen times. I do live in an area where there is no snow or rain or moisture of any kind except if you run over a toad. Which we don't have because they need water and mud to live in.
