True, there are less qualified Sprinter service places than Chev truck places. It is also true that one should not idle a diesel (any diesel) for protracted periods of time as it is detrimental to engine health due to temps being too low. This is not a problem if stuck in stop/go traffic. When you move you'll get the combustion chamber temps up. If stopped, shut it down. In any vehicle you should shut down if stopped anyway (unless you need to stay warm/cool).
There are both diesel and LP generators installed on Sprinter RVs. I have a diesel.
Sprinter engines only last a several hundred thousand miles in fleet service. Not sure if that will affect you.