Welcome to iRV2. I purchased my first DP 3 years ago. It is my current Horizon. I made a couple of mistakes I will share with you.
Review the service records first before you sign on the dotted line. I purchased from a reputable dealer and after I purchased the rig I asked for the service file. and was advised that none existed. I was forced to completely service the unit and change all fluids assuming it had not been serviced.
Check underneath for rust. My rig must have been operated in salty traffic conditions and put in storage with out rinsing the salt off the under body. I even had to replace battery cable ends where salt had wicked up between the covering and copper wires. They had turned green and harbored corrosion. It was expensive treating the rust and getting it back in shape.
I hope I have helped you at least a little;
Don & Bev Morgan Weyauwega WI, 05 Itasca Horizon 40KD, 400 HP Cummins, Delorme GPS LT 40, Toad 07 Saturn Vue AWD, Air Force One, TST 510 TPMS, Mayor of Weyauwega 2007 - 2013, Waupaca Co Board Supervisor 2010 - 2014