really the 'best' thing on bare metal is epoxy primer. but you'd need to sand off that rattle can stuff, which really should be done no matter what you put on .... epoxy primer is the only sealer coat you need, and if you go beyond its re-coat window a good scuff sanding will have it ready for whatever you choose for the next step, like a sanding primer - and always best to stick with the same brand at each step
Bill
