If you are looking at a DP, I would avoid the 2007 thru 2009 model years. I have a 2008 Holiday Rambler Vacationer XL and I have had lots of issues with the 6.7L Cummins. These were the first diesels with EPA mandated emissions controls. The EGR valves tend to stick open and soot plays havoc with the turbo. I have had to have these systems repaired/replaced twice in 4 years and roughly 16000 miles. Monaco/Holiday Rambler coaches during this period also used a hydraulic system manufactured by Lippert (or LCI) that is problematic. The electric motor, keypad, and main controller have all been replaced and now I think one of my leveling jacks is slowly losing pressure. I have easily sunk more repair costs in my HR than I had to do in 7 years with my previous MH which was a 1997 Kountry Star with the 5.9L Cummins.
Jim & Debbie
2017 Newmar Ventana LE 3436
1987 Ford Bronco II or 1974 VW Beetle