I made my own side panels. When I ordered my seats from Classic Aero Design, I bought a yard and a half of extra fabric.
I cut insert panels from 0.016 aluminum, and wrapped the fabric around the panels, attached with spray adhesive.
Then, I put 1/4" sound treatment foam (the black stuff that ACS sells) on the back of the panels, and attached them to the fuselage with 5 squares of velcro on each panel. I made a panel for each bay of skin that is exposed, and also wrapped my side pocket panels. I also used the Classic Aero arm rests in the back seat.
At the same time, I also put the 1/4" sound treatment under all the floor panels, and put some rubber-mat carpet on the forward floor ahead of the spar.
All this treatment added almost 20 lbs.
It gives the RV-8 a much more finished look, but I can not say that I could tell a difference in sound level or temperature. Maybe in the back, covering the lower side covers below the arm rests helps with temperature if the back seater happens to lean against the side. But in hind sight, I don't think I would bother with the sound treatment. Just the fabric on the panel inserts would be nice.