The Comfortmatic (Fiat) is about the same whether in auto or manual mode as it is simply a robotic gear change.
Fuel economy is governed by weight of the van and your right foot.
All the pleasure is in the driving, I'll never have a manual again.
I have had an auto for seven years. It's a conventional Mercedes 5-speed auto with torque converter, rather than an automated manual such as the Fiat Comfortmatic or Mercedes Sprintshift (no longer made). Very pleasant to drive and easy abroad since it's also a LHD.
Servicing costs no more apart from the need to change the auto fluid every few years (about 75,000 km intevals I think).
Fuel consumption may be a bit higher but that is mainly due to the gear ratios. A six-speed manual usually has a higher effective top gear than a 5-speed auto so the engine revs more slowly at high cruising speeds. More recent (Merc) auto boxes have six ratios and I think the very latest may have seven so that issue may no longer exist. Consumption depends to a very large degree on driving style, weight and (lack of) aero-dynamics so the auto box may not be the most significant factor. As an indication, my Hymer is plated at 3,800 Kg (and we usually travel pretty full); I drive with a 'light right foot', cruise around 50-55 mph, sometimes a bit more on motorways and get 25 mpg (accurate average calculated over 42,000 miles - not per tankful). That is on a 2003 vehicle with a 2.7 litre 5-cylinder engine.