Something that works for me
Took a couple pieces of 1X6 or 1X8, I forget which, angled the end cuts to match the angle of the chute to the bed, bolted them to a couple pieces of angle iron and bolted that to the chute, tapering it down from the door to 6" or so opening at the end of the chute...a feed funnel. Hopefully your chute is tall enough a 5 gal bucket will fit underneath.
While I still put my buckets in a washtub while filling, I don't have to clean up near as much feed.
Course you gotta unbolt them if you need to raise the chute.