I'm epoxy priming everything. But I see that e-coated parts don't need to be primed. However, some say that the part will match better if it is blasted and epoxy primed. What's the recommended procedure for e-coated parts (in his case the Dansk battery support and tray).

E-coat is a primer. Probably a better primer than what you can spray on.

I guess they will still need to be primed (again) because they will be welded on and those areas will need priming after the welding. So, is the correct procedure to sand the part enough to get adhesion (where it will be visible after welding; and, of course, sand it completely and apply weld thru primer within 1/4" of the plug welds on the pinched locations), weld it, then epoxy prime all that is still visible?

Red scuff pad then epoxy.

Some like to remove the ecoat.

Make sure it is ecoat, try lacquer thinner, if it rubs the ecoat off, remove it.

Epoxy primer will give the best surface to begin filler and high build primer.

the only reason the color coat would not match is if the primer is different colors or shades.
for me personally, I blasted the battery tray/support and then primed with the same primer the rest of the engine bay was painted in.

epoxy primer is just about the most durable primer and has good bare metal adhesion; I don't know how it compares to e-coat.

in regards to epoxy primer and body filler, what I've read is that depends on what body filler you use. Most are supposed to be applied to bare metal, or at least to a very scuffed primer; otherwise it won't stick well.

Thanks, guys.