I have SRW 2015 Ram 3500 (Aisin transmission) with 8ft box. I also have the factory puck system and use the B&W 3600 - ordered it from Amazon for a whole lot less that I could get it anywhere else. My setup before was with a 2005 Dodge 2500 with a Reese 16k hitch. With the new setup, I placed the B&W dead center over the rear axle as recommended by my RV dealership (B&W would not say exactly where to place it in the bed, possibly for liability purposes?). I mounted the uprights in the hitch, that the kingpin plate sits on) in the middle mounting holes. My fifth wheel rides dead level according to my 4ft level although it looks like its riding nose high. In my previous truck, I only had about 5 inches of bed rail clearance, now I have 6-8 roughly (I haven't measured). I doubt you will have a problem with how your unit rides because there is the ability to adjust things around. If the dually has a CTD, you will be mightily impressed with the truck and the hitch system. The SRW version is only available with the 3.42 rear end and even in super steep mountain terrain (Alamogordo to Cloudcroft, NM) I had zero issues. The DRW CTD comes in all 3 rear end flavors: 3.42, 3.73, and 4.10. If it is a really good deal you are looking at , I doubt you will regret it.
2013 Avalanche 345TG
2015 Ram 3500 SRW CTD/Aisin