steel saw horses, oil primer, latex top coat?

I have a set of gray steel saw horses I've picked off the curb today. I've wire brushed off the rust and loose paint using an angle grinder. I have Rustoleum oil primer, but only Rustoleum oil black, red, white, yellow, & flat brown. I do have gray exterior latex paint. If kept in a unheated old wind leaky garage, do you think the latex paint will cause the metal to rust? Or should I buy the Rustoleum gray paint?