As mentioned previously, I have taken the view not to powder-coat the chassis core. This based on the fact that mileage will be limited to about 1500 a year and I can't see me driving in the wet unless accidentally caught out in it which should be rare.
Hence, I am preping the chassis for a coating in a modern satin black specialist all weather metal paint, hard as nails and very resiliant. This has the benefit of allowing me to ensure all those little nooks and crannies are suitable well done as I'm doing it myself.
Having flattened all the welds on the floor section, a light primer gives a good opportunity to identify any bumps or dips at the mating points.