^ if youre talking about the oem rear flares.... i mounted mine with double sided tape and ONE screw that goes inside the fender well.

It holds up fine. Been through 2 winters. Rain.. sun... blizzard you name it

 

Mine has held up just perfect. There is NO need to drill into the side of the car

 

I am talking about the ones where the rear bumper is and by the rear diffuser, thanks.

 

Today, I mount the deflectors without ever read this thread. When it came to drill the four holes, I realise that the deflector hold very well with the three underside clips and the rear screw and nut, so did not make the holes and mount them with the 3m tape. They look and feel to withstand the daily use, so let it be.

 

Nice, im surprised they hold up