alright well i would teach you myself self but it wouldnt be as good as this guy. and i leanerd how to do it from this guy to.... But anyways go on the search bar and type in NOLArat and one of his threads should be about the HVAC mod. he used a new sheet of plastic but i just used the oringal one that i sanded and it still came out great.
Let me know what u think and please tell me how it goes