There is a good thread on the forum with comments from Robinson who owns a large Land Rover repair facility in New England and also owns an airstream. I'd look that up - he shares some very good thoughts on this subject. I think the title was "towing with Range Rover".
I've pulled a 2008 25' and now pull a 2017 30'. Ive used large suvs and 3/4 ton. Live in Colorado. Have owned 2 range rovers - v8 HSE and v8 supercharged. Have about 25k miles of towing under my belt - so medium amount of experience.
I noticed a difference in towing when I moved the 30' (not sure if you own one yet or if you are shopping). I could feel that it was heavier and I would get pushed around a little bit more from trucks and cross winds given the increased surface area.
I think the the TD6 would be ok if you were at sea level for the majority of your towing on flat lands. If you had the choice I'd get the LWB RR at 122" wheelbase.
But that powerplant it would be underpowered pulling a loaded 30' at 6,8 or 10,000 feet up 6-7%+ grades in my opinion. If you will tow at altitude often you should consider moving to the supercharged platform (500hp/500ft lbs torque)
Ultimately, after 3k miles towing my 30' with my infinity QX I decided to buy a 2017 3/4 ton gmc Denali HD with duramax diesel - dedicated to towing the AS. For me, it works best given my family, payload and power and braking needs here in the Colorado rockies.
You'll get lots of opinions now
like "you'll be fine" or "your crazy". Ultimately I think you can organize that vehicle to tow the 30' if you manage payload carefully and have a good, basic wd and sway deterrent system in place - AND reinforce the receiver.
It will come down to what you feel comfortable with. For me, I tried it (pulling a loaded 30' with a large SUV with 413lbs of torque and 400hp and 121" wheelbase), and ultimately decided to move up to a 3/4. It's really night and day. After saying for years that I'd never own a truck... I'm now converted.
The downside is that I now own 4 vehicles
Good luck with your decision! Fun times! Love the Range Rover.