A few years ago in Yellowstone National Park we were camped next to a family who brought all their bicycles on an extended rack on the back of their travel trailer. I thought it was a great idea and thought about doing it to our trailer but never got around to it.
This type of trailer extension can carry all kinds of cargo including a light weight motorcycle or ATV, bikes, a small amount of fire wood or whatever else you need to carry provided you can tie it down and it isn’t too heavy.
These kinds of homemade extensions are neat but caution is advised for several reasons. First, this will add weight to the axles, leaf-springs and the leaf-spring equalizers and all the attendant hardware. You should seriously consider “beefing up” these components if you do this. Second, you must consider the added length will cause your trailer to “drag” when you traverse a steep curb going into a fueling station or shopping area. So, you may want to consider adding anti-drag wheels to your extension. Third, you need to add signal lights onto the end of this extension as well. And finally, make sure the welding is professional grade and will support the weight of the extension as well as the cargo you plan to put on it. Jim