You need a 3mm plate as the footing. The tube has to be welded to this. The plate can be either welded to the car, or bolted to the car. If bolted, a plate also has to be placed under the car. There are stict regulations about the size of the plates and bolts etc... You have a fair few options for where exactly on the car the rear tubes are mounted. Mine are right on top of the rear wheel well. Other people put it close to the shock or spring mounts.