scuff it up with a red scotch brite pad, and then use a paint specifically designed for plastic such as krylon fusion.
the key is really good prep, and get it extremely clean!
Just dont get tht fusion near gas. Fusion paint and gas dont do well over time.
Here i the method I used. How to Paint ATV Plastic
Here i the method I used. How to Paint ATV Plastic
do you have any pictures of the results mud runner?