My daughter has a mobile grooming van built on a 2006 Sprinter 2500. It is similar to an RV in that it has fresh water tank, gray water tank, 2500 watt invertor, shore batteries (six 6 volt), two water pumps, plumbing, electrical etc. While we have it mostly sorted out, it has been the most unreliable and expensive vehicle to service that I have ever owned. I just purchased a 2016 Pleasure Way Lexor TS. I did not consider any class B built on a Sprinter chassis. It sounds like you are thinking of buying a new class B? If you don't like the RAM Promaster, why not wait until a class B you like is built on a Ford Transit? For every other type of conversion, they are rapidly overtaking Mercedes in sales. I believe it would prove to be considerably more trouble free, and far easier and less expensive to maintain. JMHO.
CT51