Dan, those Tekonsha controllers have an accelerometer inside and can be mounted horizontally or vertically. The unit needs to be oriented properly in either case, i,e. not sideways. Normally there is a harness adaptor that mates with the wiring for your car to the controller. Hard to say how it was installed and if this harness connector is accessible; though it could be hard wired to the vehicle also. Getting under the dash of Subaru's can be a bit difficult and cramped. You could mount the device with some sturdy Velcro or a mount that could be removed, it does need to be mounted fairly rigidly to the vehicle so it does not flop around and receives proper input as you are braking. The original bracket is such that you must remove the controller via two pins on either side, then you would need to remove the bracket itself (I'd rather hit my knee on the controller than the thin bracket). It is best to have the device located so you can reach it to make delay and gain adjustment due to a change in trailer weight.