hey im a veteran painter,30 years in the field and have done federal jobs,migs,.stealths,tanks,and also commercial buildings!!
Ok some one stated using oil based,a good polyurethane(Engine paint is a tad over board,but is basicly the same kind of paint,its more durable and will with stand intense heat,cheap isnt better,but i would for sure get a spray can of paint,do it in layers,lightly,build it up,i have a HVLP,so am ahead of the game) will work excellent,on both plastic and metal,far as the prep,on the plastic,i would use,carpenters putty,water it down a tad so you can do a slurry coat on it,so its smooth,then use unm,maybe 220 or atleast 180 grid sand paper,be careful,im doing the same thing,am taking a full tower by dell and gonna make it Rock..lol...also you can use a good polyurethane caulk,but thats a one step deal,cant sand it,and better be a pro, application wise or your screwed..i would use a carpenters putty like i said for the scratches etc,then i would use kills oil base,can get it in spray cans,then a good oil base finish,color of your choice,and watch it the nozzels will clog,the cheap ones suck..warning ok...get what ya pay for! email me if you have any questions!