I have considered having them powder coated but when I looked into this the costs mount up to about £50 per wheel. I have previously painted steels with hammerite enamel finish from a tin with reasonable results and longevity so it I thought I'd have a go with smooth hammerite from a spray can. Here's how I did it:
One by one each wheel is removed, cleaned, rubbed down properly with wet and dry and then cleaned again. I then let the tyre down so I can tuck masking tape under the rim, I carefully tape the valve and weight and then mask the tyre with paper. Each wheel is then treated with 4 coats of paint.
This is a slow time consuming process, as I write I'm on the third wheel. I enjoy the actual spraying, it is rather satisfying seeing the old marked wheel disappear slowly under fresh paint, here is a masked wheel and the result on the van.