I believe that it goes where the spare tire is. So, you would have to give up the spare tire. My only concern is that it is behind the rear axle. That means that the tank and the piping may be vulnerability either to leak or explosion in a rear end collision. According to him, Hunny bunny apparently tested the tank by shooting bullets thru it.I'll be curious about how to safely stow the tank, where, and how much cargo room it will use up.
Still, for me, i would be very hesitant to install something that has not been officially crash tested. You don't want your Outback to become a Ford Pinto. In addition, the loss of the spare tire may be a problem for those who venture off the pavement and/or distant towns far from civilization.
I think that i will wait for diesel or hybrid before installing something aftermaket such as CNG from a small time seller.