I have done this.I just sprayed clear.Spray a few real light coats first.I would say 4 or 5,then you can coat it normally.Make sure the metal is beyond clean.You should go through about 20 gallons of,I use virgin lacquer thinner,to make sure it is super clean.DO NOT USE TACK RAGS!!!They leave a residue.If you do this,the clear will not last as long as if it were painted and cleared.