We use one of the old automatic/electric feeder hoppers.
Holds about six bags of wheat, bolted some legs on to it, which in turn is bolted or strapped on the back of the quad trailer.
Just made up a bit of a chute off the back, it leaves more of a trail than full on spreading, it seems easier for birds to find plus you can see how much has gone.
It leaves us room to put about another six bags of corn in the front of the trailer too.
Just run a lead from the quad to motor with a switch on the quad.
The beauty is it can be taken off the trailer in two minutes and ready for filling hoppers or other jobs.