I mounted the proportioning valve in the rear circuit. I put some rivnuts into the subframe connector and mounted the valve so that the adjustment knob just pokes through the floor between my knees when I'm driving. And I found a rubber grommet with an ID the size of the top of the prop valve housing. I slid that into the floor sheet metal and then slid the prop valve into the ID and then bolted it to the subframe connector. I'm not sure if it is really watertight since the car never sees the rain.