I always had pretty good luck with a little touchup paint and silicon. After drilling and cleaning the filings good, I paint the raw edge and let it dry. I clean the bolts with alcohol, dab a little silicon on and tighten up.
I think I would drill, spray, dab the bolts with either silicon or something compatible with your liner material and tighten up. On a hitch where you may get movement, check the tightness. A little movement will start the rust.