When painting anything, prep is the key.
Sand down the covers before painting, making sure the whole thing is sanded nicely, maybe using 600 grit paper...
Then wash the covers in water to make sure all dust is gone, and then dry thoroughly.
Next, spray maybe 3-4 coats of primer on them. Each coat should be very light, for the first 2 coats you probably wont even cover the whole thing...!
You should then allow the primer to dry overnight, before sanding it with 1200grit paper, and then doing the same with your colour of choice. NEVER spray on an area constantly to make sure it gets covered - just keep building the layers... :thumb: