D40 auto is far better for towing.
The manuals have dual mass flywheels. Ride the clutch a little and the flywheel heats up, unable to dissipate the heat, and burns the clutch. Many manual owners have reported clutch failures as early as 30,000km - a few even less than that. Replacing it with a single mass flywheel and a HD clutch does resolve the issue.
We've towed our van for over 30,000km and we've had no grief from it. Over 84,000km on the clock now - auto still runs like a dream.
As for fuel consumption, we managed 16.5LPHK while towing 1.8T going UP the Great Divide at Easter, and that included managing some holiday traffic. Loaded (2700kg, but not towing) highway driving we've managed 10.6LPHK. Not bad for an auto with a DPF.
If you insist on a manual, expect to put a SMF and HD clutch in sooner or later, unless you're exceptionally gentle with the clutch. Some owners here are - they let the diesel do the work and don't rev+ride like those accustomed to petrol engines do.