Well, since my post I've done more investigating. You were quite right about not being able to weld them for MOTs. I've found someone doing powder coated ones for £375, but I don't want to go down that route as my experience of powder coating is that once damaged (or not) moisture behind the coating can cause rapid corrosion. Anyway some local sand blasting chaps will blast one for me and spray with zinc primer and paint for £60. I can then add what ever coating i want. I just need to get hold of a second hand one somewhere.