Here's what I did:
After paint, I masked off the joint to be about 1/16-1/8" (or as required) wide, then applied polyurethane caulking.
Then I hard-tooled the joint with a popsicle stick to an even, smooth fillet. I removed as much excess caulking as possible over the tape edge.
Soon afterwards, I carefully removed the tape.
It takes about 24 hours to skin over, 3 days to use and 7 days to fully cure.
It cleans up very easily with mineral spirits.
Since it's not silicone, it won't contaminate the paint.
Vern Little