I'm not familiar with the detail of the plastic trim on your rocker panels, but if the picture in the thumbnail in your post is showing it, level with the jack hole cap, then I'd remove it to get the Waxoyl in between the plastic and the outer surface of the steel rocker panel. Just removing the caps probably won't get you access to the middle part of the panels, and spraying into the jack hole will only coat the inside of the tube. If you want to get this stuff into the inside of the rockers, which is what will give you the best protection, get some caps that the undercoating/rustproofing guys use and drill access holes, spray inside, then insert the caps into the holes.
I'd pop the thresholds off too and spray the painted surface. Salty water gets into there from feet dragging the slush in. Winter sucks! My benz goes into hibernaton late Nov - April.

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1986 560SL
2002 Toyota Camry
1993 Lexus