We just ordered a 425 RT and will be pulling it with my chevy 3500 hd crew cab 6'6" box (tow rating 4150 PL and 17000 TW) Does anyone have experience towing this size unit with a 6'6" box? Is a slider required or suggested? The dealer said a slider not need because of the 88* corners on the 5er, but dealers will tell you anything. Any real world experience? Any Hitch suggestoons?