A lot of people do put the leaf loader on the tonuge of the trailer. I had mine on the gate of my dump trailer but I have a front-end loader on my tractor which made it pretty easy to get on/off.
Keep in mind that any trailer you make fabricate is going to have to be street legal...lights, fenders etc...at least that's how it is where I am. And registering a "home-made" trailer can be a bit of a process. I have seen swing-away hitches with a tow hitch on them too. I only used my leaf loader one season...I prefer to just grind up the leaves and bag them with my mower. If I had a dump truck instead of a dump trailer I might have more use for it.