This topic is of great interest since I recently purchased a 2002 Itasca Suncruiser 35U and am in the process of equipping it for towing and plan on using a ReadyBrake. I found a 2015 discussion on the RV.Net Open Roads Forum that has some interesting comments and information. Interestingly, my 2002 Suncruiser 35U manual is silent on the drop receiver issue.
This comment on Open Roads was especially interesting (I don't know what model/year is being discussed):
"The instructions in the Winnebago Operator's manual are exactly as the OP interpreted them. When coupling the vehicle tow bar to the factory receiver hitch using a "drop receiver" or conventional "ball mount' (commonly referred to as a stinger or a draw bar) do not exceed a 4" drop. Winnebago even includes a drawing of the receiver at the back of the motorhome with a 4" drop hitch inserted. It clearly identifies "4" max drop".
I spent several hours on the phone with a factory rep discussing this very situation. The company position was formulated after several incidences where longer drop hitches were used pulling either a vehicle or a trailer without auxiliary braking systems. In a panic stop situation the added leverage of the longer drop in combination with the lack of auxiliary braking systems caused the hitch to either fold under the frame or be torn from its mounts.
During our conversation I mentioned that by imposing this restriction Winnebago was severely limiting the vehicles that could be towed. After repeatedly inquiring what could be done to remedy the situation I was told that Winnebago no longer buys commercially available hitches. In 2012 they started manufacturing and installing their own proprietary hitches. They are a minimum of 50% stronger than any commercially available hitch. He also backed off a bit saying they had been extensively testing 6" drop hitches and found no problem using them. I haven't looked at the 2015 and 2016 owners manuals to see if they have changed their recommendations."
Here's the link to the Open Roads thread FYI:
https://www.rv.net/forum/index.cfm/f...print/true.cfm