Well you want it somewhere where it will be protected from getting sheared off, while also not being in the way. Sticking thru a rear bumper by the plate would be good. Likewise inset inside a front grill using an angle bracket as the mounting location, with just enough protruding to allow you to manipulate the coupling.
I'm intending to add a 3" mandrel bent pipe as a front bumper guard addition to a full brush guard and intend to cap the pipe and have fittings inset in the ends to utilize the pipe as a air tank.