You might need to click on the image to see it clearly (not very well sketched)....but essentially the modification I propose is one which will stop the plastic getting snagged as the monopole slides in between the two splinting plates (no idea if they have a proper name). A single sheet of plastic is heated and formed around three faces of the monopole (the rear and two sides), then the holes drilled out again....and the plastic countersunk to avoid bolt threads snagging it. Incidentally, I have drawn it too short...it needs to be long enough to accommodate both monopole bolts.
An alternative mod Dave Broom suggested was that the plastic be stuck inside the splinting plates, as Ben designed it, but that it have a flange. What is encouraging about the fact that Dave had been thinking about it, is that it meant that others had encountered this problem; not just me rigging badly. I think this probably happens anywhere that rigging is being done outside a hangar......the slightest wind getting under a tip will make the monopole twist as it slides between the splints.