Hi everyone.....Ive always assumed filler had to go on top of epoxy primer, or surfacer, or 2k primer because filler traps/holds moisture and it would be leaning right on the bare metal. Lately Ive seen filler going on bare metal, then a primer surfacer over the filler and bare metal. Im just a weekend warrior doing my own thing on my own cars, so Im just wondering everyones opinions/preferences. Thanks!

You can go direct to metal or over epoxy primer. Either way is acceptable however there seems to be real benefits in in applying epoxy primer first.
The epoxy seals the metal and keeps it moisture free, has rust inhibitors, and bonds very securely to the metal.
Here's a video showing results of an individual's test results: https://www.youtube.com/watch?v=-yA8q4K ... redirect=1

I find rust under filler all the time when stripping cars for restoration or repainting. The extra step of applying epoxy primer makes sense for me when preserving cars. However the customer's budget must be considered as well.

Hi watchdog,

It depends on which DTM (direct-to-metal) primer you're using. For instance, if you use self-etching primer, the filler should go on the metal first and then spray the self-etching primer over that.

If you are using epoxy (which as a DIYer, I prefer) then I like to spray the metal first with epoxy (to seal it), apply filler and then even spray epoxy over the filler to seal it. Just keep in mind the re-coat window!