"sink and shower are ABS; end-cap is fiberglass."
All are ABS. I used krylon fusion on my end cap, outside of the trailer in a garage. Overspray would be an understatement, the way it sprays it seems to want to go everywhere except where you want it to. Just about everything in the garage ended up with a white 'dust' coating, so mask and cover anything you don't want getting paint on it. Cleaned and Prepped the heck out of it not to happy with how well it's stuck or wears. Others have been happy on the forums. Used much other spray in the garage with no overspray like the fusion. Watch the dry/recoat times. I'd recoat well under 24 hours if you do. I did mine at about 20 hrs and got alligatoring. Then you have to wait. 7 days to recoat. Thought I'd use it as a primer and paint over it with something else, krylon said only krylon fusion would stick on the krylon fusion, though others have reported success covering it with other paint. Wished I'd just used a plastic primer paint that rustoleum makes and then could paint with whatever I wanted.
"looks exactly like mine...I'm planning on using por-15 white coat on the ABS".
About at this point, planning on using the white coat on my bath surfaces as well after I get them spray primed with an automotive plastic primer.