polyester fillers over etching primers

I have completed the new bed for my roadster pickup (the old bed was so thrashed that all I saved was the tailgate). The new bed is all made from #14 and #12 ga. cold rolled steel. I now want to paint this sucker, and I want to use an "etching primer" to give the best adhesion to the bare metal. There are some places on the new bed that will probably require a bit of polyester filler, or 2-part epoxy putty for final cosmetics (hey, I'm not Ron Covell). I have been studying the various websites, and there seems to be an opinion that you can not use polyester fillers over an etching primer. My plan was to shoot the entire bed with an etching primer, let it dry for a day, then spray the entire bed with a coat of old traditional red oxide primer/filler, ---the stuff you mix with laquer thinner, not the new 2-part stuff. Then I would use a 2-part epoxy spot filler to fill any minor imperfections. If I see any larger spots that require polyester filler, I would grind off the etching primer and primer filler in that area only, fill and featheredge, then reprime with the red oxide in that area only. This may seem a bit backwards, but A---I don't want to do the spot putty / polyester filler thing right away, but B--I don't want the bed to rust between now and when I get time to do the spot putty thing. I prefer to use Dupont paint, as I have had success with it in the past, and I will probably use acrylic enamel as my final paint (maybe by end of this summer). I know there are newer better paint/primer systems available, but I am comfortable with the old style primer systems, and they're a heck of a lot cheaper. Any good advice would be appreciated.

Brian,
I would stay away from the lacquer base products as they dont have the logevity as does the 2K products.
I am a PPG man of 30 years and would reccomend
using DPLF- sealer over your bare metal , then you can use PPG's polyester putty that is formulated for their products , then shoot K36 for your filling primer.
I know the products are high dollar but well worth the price in the long run, the red oxyde lacquer primers dont have the holding qualities, are you going to use base coat /clear coat over all your work? If so I would highly recomend using the better products as the new paints arent really made to go over the old style products.
ONE thing i do stress is dont mix and match paint products as it can blow up in your face and you will never know why, some people do it all the time and never have had problems , but why waste all your hard work if it doesnt work? then you have to do it all over and then you have to buy more products to do it all over and saved NO money if you have to do it twice!
SprayTech