Pat, a base coat of a metal primer is recommended before applying a
paint (my experience is in marine use -- a pretty harsh environment!)
Metal primers are available in spray can form at your local hardware store
and they also provide a "smoother" surface for your exterior paint coat
I've had good luck with an aluminum tiller.  Primed well and painted with
an enamel paint, it has been exposed to the weather for 6 months and
I've had no problems.
 
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      | Kathy Murphy - National Air & Space Museum |
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