I had a zetec s withe the front and rear extensions but no side skirts
I bought some genuine ford ones and got them painted. They came with fixing clips like the ones for the door cards which push into holes in the sills (which obviously my car hadnt got) and also two other clips which pushed up into the floor after removing two bung like things.
I used automotive grade double sided tape to fix the top of the skirts. They have been on the car nearly 2 years now and havent moved