Scrape. Wire brush. Scotchbrite. Wipe down. Paint.
Repeat from 3 ad nauseum.
So far have done two fuel tanks (added first stage of Nitromoors), six floor sections, two fuel tank hatch covers, and the ducting for the engine breather. The floors may actually be finished today! Then we get started in the engine room itself, plus I get to scrub out the hold, where the bright newly painted surface we left is not all covered in rust again.... But never fear, it's only from all the grindings when the knee were done. I've just ordered a load of timber too, for the hold floors and new top planks.