bob vila doesnt know shit about painting steel front doors, if you want a steel door to last longer then any warranty that the manufaturer could possably give you use a xylene based industrial enamel you must find a skilled painter that knows his shit with an HVLP.
i have doors out there that i painted 10 yrs ago that still shine like the day i painted them.
they are not only rust proof but can stand up to the toughest kid