What paint are you using? I have been spraying SEM Color Coat over a medium-wet coat of their Sand Free Adhesion Promoter per SEM's instructions. I have also been cleaning the trim pieces with their Plastic & Leather Prep beforehand. The top piece of my steering column cover was badly deteriorated from sun damage so I sourced a replacement on eBay, it was black but I cleaned it real good and then hit it with the prep spray and then the color coat and it came out great. Took 5 coats to get the saturation where I wanted it, but that's alright. I also just painted some LMR-sourced replacement scuff plates and I ordered those in scarlet red which only took 3 coats to cover.
I did a test yesterday with another can of SEM Color Coat that I had on hand, this one in Napa Red. I'm going to replace the rear package tray which on my car was just the fiber board with a coat of color on top, no carpet or upholstery covering it, I'm guessing this was factory. I sprayed a piece with Rustoleum gray primer first and then the Color Coat over top, and also sprayed a section without first applying any primer. The piece with no primer did better than the section with primer. No prep spray on this piece since it's not plastic, just fiber board. So I'm real curious what type of paint you're using for your quarter trim since I'm going to spray mine soon and they have a lot of sun damage and variation in texture and will be the most degraded plastic pieces that I've yet tried with the SEM paint.