To size these things properly and get the holes in the right place the best way is to play about with a bit of cardboard and scissors, however as you will see from the pics you can make full use of the existing screws on the inner liners and there is no need to drill.
Pic 1 showing a view of the rear flap from behind
and a view showing the inside which if you look closely you will see two screw heads from the original liner screws which secure (these two are more than enough to hold ), sorry about the crap, they are mudflaps after all!
Now a view of the front from the rear
This was deliberately sized quite wide to stop crap from being thrown up against the rear arches
And from the other side
Again if you look closely you will see the two original screw heads, in this case one is towards the inside edge of the flap and the other about two thirds up on the left. Now with the front I have added a small stainless spring clip and the top to keep it in place. This stainless clip is one of these re-usable clips for holding sheaf's of paper together. I used one which will clip about 60 sheets of paper so that it was big enough to go over the mud flap material and clip onto the inner wing. Arrangement works perfectly and is the same that I used on my S3 for tens of thousands of miles without falling off!
Not as neat as factory fitted I will agree, but just as capable, if not more so (as I sized them bigger) at keeping some of the stones and crap of the bodywork and given that the factory dont make them anyway, its the only choice at the moment.
Hopefully some will find useful
Cheers
