These are self-contained units i.e 1x back and seat pad per seat, with the fuses and relay wired in and multi-plugged up. However, as I have all my relays in one place I replaced the supplied [stand-alone] relay holder with one on the supplementary relay bank. This is to keep everything in the same place and secured properly.
Ran the wires to the seats along the bottom ridge in each respective seat area (the bit where the floor joins the angled side panel), and connected up to the 12v live, 12v switched and gnd buses. 
Operation is by individual switches mounted on each side of the dashboard, just by the doors