Regular inspection is the best approach. The triangles at the corners of the bulkhead seem to be vulnerable, and if you have a small drilled hole in the upper layer, fill it with ACF50. Forward facing sections of the chassis get gravel rash. The most vulnerable is the double skinned crossmember behind the seats.
Black Dinitrol will protect it. I asked for the honey coloured wax coating, because it's easier to see what's going on. The autophoretic coating is not powder coating and my experience is that it doesn't lift like powder coating. The gravel rash on mine has stayed as pinpricks on the coating.
Nothing beats regular checks. It's the same with the galvanised chassis. Better protected, but corrosion can still get going, and produces a white powder.
I use two aluminium deflector plates over the exhaust mountings, to keep the crud off. The front section is angled upwards. The main section is horizontal. The angled section is blasted by road grit, as if its been grit blasted, which it has. The horizontal section is untouched. So the forward facing sections of the chassis get blasted constantly by road grit.
