I have been searching for a long time and I finally found an old fridge to build my first smoker! I am super excited. My roommate is helping me out and so far we have the guts out and the insulation out. We are making this in to a charcoal and electric smoker so we can do either or. We have bought the smoke stack, sheet metal for the door and to seal where the installation was, along with a few other basic parts. I see that some of you left the old insulation in and some of you put new insulation in. I wanted to be safe and rip the old stuff out, but I was wondering if I really need to put new stuff in or if I can leave it with out any and then seal it up. What difference does this make?