After the 2 coats of clean metal primer I could see the edges of the marine-tex patched areas. I wanted to fix it, since the areas in question will be above the waterline.
I first tried to sand the edge down some more. But it seems that once the MT gets to a certain thinness, it does not want to sand anymore, and instead flake off.
Then I thought "well if I could build up some primer around it, I could sand that down to make the transition disappear". So I bought this stuff, in order to get maximum "build":
Bad idea. This stuff is completely incompatible with marine tex. It does not stick well at all. So I spent the last several evenings sanding off the primer that didn't work, and eventually applying several more coats of the clean metal primer with the HVLP gun, only in the problem areas. After about 3 coats I was able to sand away the edge of MT vs aluminum.
So tonight I finally got the first coat of white on.
Even though I'm inside, this thing is a bug magnet. I have at least a dozen gnats to sand off tomorrow before going further. Not sure how I'll keep them off the final coat, though.