My experience was the opposite: underneath a heavy duty marine expoxy paint and primer, I found bare steel on a Genesis HP 100 I bought to double up with a hotdipped one I had. It took days to get the whole thing totally stripped of that crap, but it started rusting all over just as soon as it was stripped and exposed to the moist, salty Hawaiian air. The zinc-rich cold galv I sprayed on is not the most scratch resistant coating I've ever seen...though the galv is doing what it's supposed to, because despite seawater and suboptimal rinsing, several scratches down to the steel aren't rusting.
Still, if I had it to do over again, I'd sell the painted tank and wait for a galved one to show up.