Video of B&W Flex

Where are people getting the idea that the bed supports the hitch? That is ridiculous. It is a gooseneck hitch that mounts under the bed to the frame using very large bolts. The Companion is the RV adapter that fastens to the 3 inch square steel bar coming from the hitch through the bed. With the proper hitch for the vehicle, they have different ones for each make of truck, installed properly the hitch holds the weight. I see no possible way that a properly installed hitch and Companion could ever cause the bed to flex unless there is a problem with the vehicle itself such as the frame flexing. Any flex in the vehicles frame could possibly allow the entire unit to flex or possibly the entire unit is vastly overloaded but that would be unlikely as the hitch is rated to 30K.
To the OP I would verify that you have the right hitch for your vehicle and if it is correct verify the torque on all of the 3/4 in bolts that attach to the frame. If either are wrong you potentially have an accident waiting to happen.