I don't know what kind of car you have But I had a 94 civic an what I did to mount my 12 gauge in my car was ...take the rear seat out, remove the fuel pump access cover an unplug the pump, an fuel lines...Then jack the car up an Take out the two straps holding your gas tank, then lower it down an remove the tank slowly...Once you got the tank out tank a grinding tool an smooth the under body once you have done that ,Go up in the rear of the car an drill 2 holes on oneside then 2 holes on the other side to mount the long gun, Now Put your long gun under the body of the car an strap it with exhuast hangers an bolt it in....Reverse all that I said an you have a good anti theft, an a spot to mount your Long GUN .I hope this helped Joshua