If the OP is going to tow get a V-10. Anyone who complains their V-10 doesn't have enough power needs to get to the gym and work on strengthening their right leg and then start using it.
:B
Unless a V-10 has something seriously wrong with it {not likely}, it requires no, none, zip, nada after mark garbage to make it pull like a freight train{just put your foot down}. If reliable, bulletproof and can be serviced just about anywhere without refinancing the coach are high on your shopping list... then get a V-10. Yes the mileage will be single digit {who cares it is an RV}, I consistently see 9.5, YMMV.
Yes the Mercedes diesels get 16/17 mpg {and no, they don't get better than that in the real world}, and you can look forward to recouping your initial investment in about a quarter of a million miles assuming you never need to have any work done on it...
As always.... Opinions and YMMV
:C