How to Initially mount fender skirts?

I bought my 2720SL used and the fender skirts were missing. Just ordered and received two new ones from Trailmanor. They do no have any mounting holes drilled nor does it appear there are any attachments for mounting. There is a lip around the curved portion. How are the fender skirts mounted? I read earlier they are to be screwed in but to what? There are screws around the wheel opening attached to what looks like rubber molding. Thanks in advance for replies.
v/r
Roy