Do you already have screw holes in the rear bumper from the old plates? If so then I suggest putting the plate holder on the rear, then use the screw holes already there to secure it in place, then put the number plate in, and secure with the remaining part of the plate holder.
For the front I have done the magnetic number plate holder trick, which so far has worked just fine and looks pretty cool too. If you don't want to do that then I found that the Halfrauds double sided stickies work very well/
