I have a question, is the hump under the passenger
seat the ventilation for the a/c-heater?? can I mount an amp under there??

 

It is the heater vent and yes you can, let the back end of the amp sit on the vent and rasie the front end with long bolts with nuts to make it level. That way your not in the way if air flow. I filed a point on the ends of the bolts so it sticks into the carpet and does not move. Look in my gallery for pictures.