If I needed air flow and had a big vehicle with room I would find a squirrel cage fan, make my own enclosed radiator and mount the fan high with a four inch tube from Home Depot going to the radiator. The type of aux fan on cars is of that type because of limited amount of room and need to not block ram air . You are watchin the temps... just fuse it and put an on/off switch for you to control.... a temp activated switch is just one more thing to go wrong when you least want it to.