I'm not sure if there is room under the front passenger seat, maybe look into that. Just make sure it has breathing room. I advise you not to mount it to your subwoofer.
My favorite place is the back of the rear seat. Maybe do that and get a roof rack for the camping stuff?
Also keep in mind, a lot of amps don't like being "grounded out" by being screwed directly to metal. If the screw holes on your amp are plastic, this isn't an issue. Just make sure the metal of the amp isn't touching the metal in the car. If your screw holes are metal, use some rubber grommets in the holes.
I'm all about sharing the road with other drivers - as long as they use the part that's behind me.