Does anyone have any experience mounting a trailer hitch on a 2005 X350 XJ8L?

Do you already have the hitch?
When I install hitches they come with instructions for the car they are made for.
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I don't think that they are available because of the air suspension

I believe they were a specific kit accessory that also included the additional wiring harness and some relays to insert as the rear sensors needed to be disabled when a trailer was attached.
You will also be cutting into the the rear dress bumper cover to give the hitch clearance.
There are a couple of threads when you search "Tow bar" X350.

The air suspension is not hindering the installation of a trailer hitch (or towing hook, as I would call it) . On the contrary, it helps keeping the car lever with a trailer attached.

I have also been thinking of installing a hitch, because in SV8 form the car is allowed to pull 1,900 kg, which is quite nice,

But:
one thing is that hitches for the X350 are very rare, and the only one I had found here in Germany was around 2,000 EUR, including the electric interface needed to connect it to the bus system. That's not worth it for me.
The other is that you need to cut a hole into the rear bumper cover, and the lid to cover this hole when the hitch is not in use is not available any more.

Best regards,

Thomas