Hello Aussie Mark, welcome to the world of caravanning.
Not sure what you mean by an "off road caravan" and the weights you quote, particularly the upper end is likely to be too heavy for a Range Rover Sport to tow sdafely.
You need to check the kerbweight of your RRS to determine what the maximum weight of the caravan can be towed which should not exceed 100% of the tow vehicles kerbweight. Additionally the caravan should not be wider than 2.3m.
Remember also that if you passed your UK driving test after 1st January 1997 there are restrictions on the combined weight of the outfit that should not exceed 3.5tons unless you take an additional driving test to obtain a B&E licence.
If in doubt put a call out on the forum for cris or Lutz, both have a more detailed knowledge of the laws related to weights and towing restrictions. Mal