[svxistentialist]

That sounds good too Tom.

Tony's best bet may be to remove the front and the rear of the plastic liner, and hopefully leave the upper one in place.

From my own experience most rubbing happens on lock, to the front and rear plastic. If you could cut the front plastic narrower than standard, then find a way of fitting and securing* it farther forward in the arch, that will probably stop the worst of the rubbing.
* It will need securing. Wind from road speed will blow it back otherwise.

At the back, there is no room to move back with the plastic. He may be better removing that part, and protecting with the flashing or the spray you mention.

Joe