Adding big deck/ extra axle to a 5er. Carry 4 motorcycles.

fj12ryder wrote:
The swivel wheel platforms pivot so both wheels are always on the ground, they are not mounted solidly to the trailer.

You mean the hitch articulates about the axis of the hitch receiver ?

The only thing those wheeled trailer extensions don't do that a 2nd trailer does do is articulate left and right. They are essentially a trailer. The fact they are connected to the 5th wheel via a hitch receiver makes them look even more like a trailer.