Like said get original towbar or the same Westfalia from PFJones. Wiring for the original module is there in the trunk.
https://www.pfjones.co.uk/bmw-x5-e53...le-towbar.html
All E53 3.0d models have Webasto from the factory. Without additional equipment it only works as additional heater when engine is running. This can be quite easily coded to work as a pre-heater and used from nav screen or MID unit depending which you have. There is also a possibility for remote control. The wiring from webasto to original receiver's location in the trunk should be pre-wired. Here is the remote set I installed on mine.
https://www.carsystems.eu/bmw-x5-e-5...ter,id568.html