You can unclip the plastic trimming between the carpet and doors. Start by unclipping from the front and then they come off easier. Might need to undo the front seat belt bolts but i managed to squeeze the cables through, then out of the trimming under the rear seats for me was easiest.
Ran the RCA and amp switch leads down the drivers side, and power cable through the bonnet cable whole and down the passenger side. Then earthed it at the left rear seatbelt bolt. Was easiest place to earth for me because I did that in my last clio and all was good for 3yrs.