Can't reallly load a Mule up like and atv... that is kind of an issue.
The problem I see with a stock trailer is you have to wash them off every time you use them, keep them in a covered area, ect.. if you want them to last for any number of years.
As for unloading hogs off the trailer that would probably depend more on where you unloaded them to. IF you had a pen or some thing at your house that you are typically going to unload the hogs to you could build a ramp style shoot to match what ever the set up is on you trailer.
Just throwing ideas out there... maybe some thing will trigger other ideas...