Measure the height and width of the panel, and mark the center of each panel with a pencil or marker. Apply double-stick adhesive at the mark, and attach the retainer clip. Repeat this process for each panel. Attach two retainer clips for large panels.

Use the previous panel measurements, adding a couple inches to the height and width, and cut the insulation to size using a straightedge and utility knife and wearing rubber gloves and a respirator mask.

Starting at one edge, tuck insulation into panel frame. 

Once insulation is in place, find the previously-attached retainer clip in the center of the panel, and poke a small hole with a utility knife. Allow the clip to poke through, and press the other half of the clip in place until you hear a click. Continue process for the rest of the panels.