Might be worth giving Steve at Rainbow a ring.
They were going to powder coat my front engine cover to see if it would be better but have decided against it after trials.
They said they use a company at Parkgate, Rotherham who are quite good.
Hope this helps.
Sam -- Nowhere near Sheffield , but they are reputedly the best there is , so perhaps worth a call ?
Speak to Andy , who is sound as a pound and has always delivered a first rate result , over the past 18 years that I've used them for my powder coating that is .