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can't help you too much with specifics...this is a unique tow vehicle, and has generated some controversy in the past, but I'm pretty sure there are a couple of Toureg owners here who might be able to help.
Some of the numbers with this vehicle just don't add up. There's nothing "out of line" about the Airstream fleet's hitch weights; Any trailer, of any type, should carry 12-15% of its gross weight on the hitch; otherwise, the combination would be dangerously unstable. So for VW to claim a 7700lb max towing capacity, with the limit of 616lbs on the hitch just doesn't jibe. You can't have 7700lb tow capacity without a minimum of 900lbs on the hitch. some might say "10%"...still, that would require 770...
My understanding is that this vehicle has a special hitch, and a self leveling suspension that precludes the use of any weight distributing equipment, also...so that's of no help.
Unless I'm missing something, (which is entirely possible), it seems that with a 600lb hard-limit on the hitch, you're really limited to a trailer that weighs no more than 5000lbs, gvw. that's the trailer, all its options, and all your stuff on board.
yes, the hitch weight will vary some based on how the trailer is loaded, (too much or too little fore or aft) but you don't want it outside that 10 or 12-15% range.
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC