Not a lot of information to go on to comment.
Diesels are available in class A and C (and Super C).
Do you know any of your requirements (floor plan, length, towing capacity, budget, new or used, planned usages -part time or full time, towing etc)
If your only concern is mileage, yes diesels do get a bit less MPG and cost slightly more to operate, but the trade-off is that you usually get higher end finishes, greater towing capacity and overall great reliability and generally better handling/ride due to the airbags.
I get roughly 7-8 MPG on my 2003 DSDP.
Let us know more of what you want:B.