I never put air freshener on my pick-up from the time we got it brand new, never smoked, and i keep the inside clean. 5 years down the road and some peeps were still saying it still smelled fresh and like new (but di naman yung new car smell).

Best is to detail it, get the A/C system flushed, put some charcoal or those absorbent thingee (i.e. Thirsty Hippo) and keep the inside clean.