Use Testors Putty instead of plastic filler. Auto body filler is too tough, you'll sand away the plastic before you sand away the filler. Putty is available at hobby shops... it is used to modify model cars. Think of it as "body filler" for plastic models.
Stay away from Krylon Fusion. I've used it before and the paint spiderwebs at the first slight impact. You're better off sanding the base using 600grit sandpaper, then following up with a light coat of laquer primer, sanding that smooth, another LIGHT coat of primer, another sand, then your topcoat. Lots of work but anything done quality is.
good luck!