I just turned 21,000 miles on mine this last weekend when we went to the Mojave to ride offroad and camp at Jawbone Canyon. Two bikes inside, all the crap two people could never use for camping and tons of room left over. Mine is the medium length, tall, passenger version with windows and rear AC.
Loaded down with everything going 80 (on the limiter) in 105 degree weather with both AC's blaring, I get about 18 mpg. With a trailer with two bikes, minding my own buisiness at West Fest last year I got 22mpg. Around town, regular city driving I get 22 -24. The thing is 9.5 feet tall, those numbers are very reasonable. On our trip to Mojave, I blew a Turbo Resonator http://www.riordanco.com/projects_success.htm
and went into limp mode
luckily the next dealor was in San Bernadino and this VERY COMMON failure was a snap for them to repair and they had the part in stock.
I Love my Sprinter very much. It has been on so many trips now and works so well. I have some ideas for customizing the interior for function (water supply, heated water, sleeping, window netting, etc) and keeping the total versatility that I enjoy so much now.
At Skip's Blood Moon Bash