I couldn't find anything suitable over this side of the world for either my 2011 Passat wagon OR the 2014 Treg. So I ended up buying a fitted boot liner for each from Titan Covers in the UK.
Volkswagen Boot Liners - Titan Covers
If you contact them they will do a VAT exempt cost including freight to Australia. They can be a little slow with the email and so I ended up calling them one evening to chase up. After that, it was all systems go! I think mine were about 200 pounds for both
liners including express freight to Perth. They have split rear seats to match the division of the rear seat in the car and a bumper flap which folds out over the back of the bumper when the tailgate is up. There one minor inconvenience in the Treg and that is the interior lights on the left and right side of the boot and the raise/lower air suspension switch and 12V outlet on the right side are not tailored in the boot liner. Not sure if this a subtle difference in Euro models or not. If I was really anal I'd get the sewing machine out and make a cut to expose the lights and switches/outlet and stitch them up/overlock them again. But I'm not. I just pull down the RHS flap to expose the panel if I want to use the 12V socket (for the Engel) or use the suspension settings to lower the back (hooking up the van for example). With a shepherd we needed the extra protection for the cars and these liners definitely provide that. I'm very pleased with the Passat AND the Touareg boot liners.
We tow our van (not quite a large as yours - ours is a 21" Coromal full-size caravan @ about 2.5T) and get between 13.5 and 16 l/100km as well depending on driving speed, wind conditions etc. My worst has been 16.8 in the Treg, (big headwind) which if I had been towing in my 4.8l Petrol Ti Patrol, would have been about 30-35 litres/100km. My worst in the Patrol was near Geraldton in the face of the usual massive crosswinds/headwinds, and that delivered a consumption of 35 l/100km!! Around town without a van it was about 15-18. It was a truck - a nice truck, but still a truck...
Ours Touaregs are amazing machines. Daily driver, tugging a load behind them, or out in the bush. A truly under-appreciated vehicle (at least on this side of the world).
If you want some images of the boot liner fitted, PM me and I'll see if I can take some tomorrow.