loose ski pylon

I have an '88 Sunsport with a loose center ski pylon. I keep tying to tighten down the floor cover plate but it keeps coming loose. The pylon does move slightly during use and it seems to be loosening up the floor cover plate. I have checked and tightened the adjustments under the floor but still no luck. Any suggestions on how to fix this?

Is the pylon itself loose or just the trim ring? If all 4 set screws and lock nuts are tight and the pylon is tight in the cup, then just rotate the trim ring, predrill the holes and screw it back down