Ok, here's the deal.... if you want to apply any coating to the black textured plastic parts on your bike (including the saddle bags) theres a couple options. Option 1: this is the quickest, cheapest, and easiest method. Krylon fusion, prep with first a good hot soap and water scrub, dry, wipe down with alcohol, a light scuff with a grey scuff pad, wipe down again and apply multiple light coats with a final medium wet coat. I've used this method to restore all the black plastic on the lightning ss I had and it held up great!
Now option 2: this will work whether you want to paint it to match the bike or bedliner or or whatever. Wash with hot soapy water, buy a plastic prep cleaner ( basf rm 902), clean with that, give it a very thorough gray scuffing or can use red if you're going to apply a high build 2k primer surfacer. Clean again after scuff. Apply adhesion promoter compatible with your primer (bulldog is available at auto parts stores and works well with most primers). Apply primer surfacer (aerosol or 2k). Sand and repeat as nescarry in order to bury the texture in the plastic (if you're going for smooth paint, for bedliner just scuff the primer and go for it). Then apply desired finish.