I would shy away from an HDT for the floowing reasons. The fuel efficiency will be a bit better but not good enough to justify the added safety and towing power. If you pull in a hilly or a mountainous area you will need and like the extra power.I have see that they are easier to drive. If you are looking for a used truck the MDT's were often used for city delivery and show the ccorresponding wear.
I'm interested to see how this turns out as I am talking to a non-profit about building them a mobile learning ccenter (essentially a coach for learning).
Good luck
Tony Desnick
ToolSet Motorhomes