Installing additional stabilizing equipment on your Discovery is not necessary as the vehicle is already designed to withstand the load created by the trailer and hitch system. Adding stabilizing bars or chains to the vehicle will increase the torsional load on the hitch, possibly causing it to be ripped off the rear of the vehicle. This is not absolute, but is a possibility, so is therefore not recommended. In addition, please remember to adhere to the maximum weights listed in the owner's manual/discussed in the last e-mail and use only Land Rover approved parts and accessories.
I have consulted your vehicle owner's manual and as we are not a technical facility, the only information I can confidently provide to you is that listed on pages 146-153 of the manual and the description above. For any specific questions or recommendations, you will need to consult the service or parts departments at your authorized retailer. They will be able to explain this issue in greater detail and answer any other specific questions you may have.