Just lay them in there. But you might want to try and figure out a way to keep them from cutting the carpets. I had mine in for about 40k and it cut threw the carpet. Right by the front of the drivers seat and around the sides. the passenger side did not do that but I assume it is because the X-girlfriend didn't ride with me that much, and the buddys were drivin there own wips.
I have had mine for a while and haven't had any problem with them cutting the carpet. I just set them in and they don't seem to move around to much. The guy that made them left it a little rough around the bottom so it would catch the carpet and not move around.