Basically, My tactic is to sand or blast to bare metal and immediately spray small batches of epoxy primer the same day as I complete the metal work. I spray epoxy in a heated garage of course. I will get the garage up to at least 70 degrees for 24 hours before I plan to spray and then I keep it at 70 degrees for at least a week after. Any body filler I use is on top of a layer of epoxy primer within 4 days of spraying the epoxy due to the chemical bond between the newly activated primer and the filler. . If I go 5 days outside the spray window, I will spray another layer of epoxy to reactivate the primer window of opportunity. I am in the camp of those that believe that only epoxy primer should be touching bare metal. Fillers go on top of that and get sealed under a sealer. Basically I follow these instructions from my favorite Epoxy company- https://www.southernpolyurethanes.com/perfectpaintjob. I just stay far away from the window limitations by going 5 day window instead of 7 day within reason. The good part of spraying in the winter is the relative low humidity in the cold air. As long as I get the garage up to temp, I really have no issues. The paint will not come for some time. Hell, I might just get the car in epoxy, do the filler, epoxy sealer and then leave it that way but use a vinyl wrap for color! Maybe change it every couple years. I dont really have the skill or place to spray a proper clear so until I can get the skill an/or location, this is what I have to do. Lord knows I dont want to pay someone else to do it. I am not cheap, I am a DIY guy.