Thing is, I'm not too concerned about surface corrosion on the chassis.

It's the rusting of steering arm etc pictured above. I hoped for that stuff to be replaced rather than waxoiled.... 2022 P440e AB

With the nights drawing in and winter opportunities to do that sort of work approaching and less inviting- i set about 'doing' my 08 RRS yesterday afternoon and into the early hours of the evening. very satisfying, dealing with heavily corroded areas such as the tank-guard and side-step mounts. the diff casing had absolutely NO paint on it- and I applied copies stokes of black Hammerite- doing the chassis rails as I progressed back to forward. Lack of light and the bulb blowing on my halogen stopped the task but id say 2/3rds of the car is done now. i had an advisory on a corroded rear brake-pipe. i put rust neutraliser on it and a dab of hammerite.
satisfying feeling- its what we all did in the 60's/70's to our untreated Fords/Vauxhalls/BMC....