I about to install a Kicker ZX350.4 to run all four speakers and I was looking at putting it under the front passanger seat where after measuring there is enough room to mount. My main concern however is running wires under and around the floor carpet, is there any risk of fire or any other problems that come with running wires in this situation?
nope. done it for 20 years. just try to keep the power lines run away from any ignition source or crossover module for speakers. These can induce noise into the system. I tend to try to keep the wiring either tucked under plastic trim pieces like the door jamb seals and paneling, or if I go up the center, I tuck the wiring into the edges so it isn't noticeable under the carpeting.