The tunnel plate is intended as a heat barrier between the exhaust and the torque tube, but during the C5R race car development the engineers realized that a thicker plate reduced the torsional flex in the chassis. With the introduction of the C6, the tunnel plate thickness was increased from 1.6 to 3.2 mm
The torsional rigidity of aluminum increases with increasing thickness as the larger cross-sectional area results in a greater resistance to torsion.
With the tunnel plate removed for servicing the drivetrain, this was a nice opportunity to upgrade. The Elite Engineering and TPS Motorsport tunnel plates became all too expensive when adding overseas shipment and import taxes, so I sourced a used C6 tunnel plate from eBay ($59 inc shipping). Except for the increased thickness, the C5 and C6 plates are geometrically indentical, so upgrading to the C6 tunnel plate is plug & play.
To reduce heat transfer from the exhaust pipes into the center tunnel, I added a thermal insulation sheet with adhesive backing.