Technically the carbon on this LMP2 should be a good ground plane for the 1⁄4 wave Radio VHF antenna. Unfortunately, the resin and poor bite into the material often lead to a fairly average ground plane.
Adding a copper or aluminum foil ground plane can really help you get the best match and minimum signal reflection from of your quarter wave on your carbon tub. If you are using thin tape to build up your copper area, ensure you are using materials with a conductive adhesive.
Once installed, use a multimeter to check the resistance back to the connector at the transmitting device, we are looking for a few ohms maximum. For the purists, yes the resistance check is not a good indication of the true impedance but it will identify failures and very poor connections.