Yes, good contact point is a must. Sand down the paint to the metal. I would mount the battery in a box on the passenger side of the boot. Run the wiring down the drivers side and then across in front of the petrol tank and to the left side of the boot. As noted above, make sure that it is not rubbing on any metal and/or sharp edges. If it has to go across a sharp edge, use some rubber sleeves (cut some rubber hose down the centre) and wrap it around the cable. Use cable ties to secure it in place.