Decades before those corner feeders came on the market I just made a 30x60 “wall” that I put in the corner to make an easily cleanable corner hay bin.
I took a 30x60 3/4 plywood, framed it out on all 4 sides with 2x4s, stained and applied spar urethane so it looked nice. Added two small screw eyes to one side, two eyes to the stall wall and used 2 small snaps to attach. This was before the zip tie era and that’s what I would use today instead of snaps. The other side was just another screw eye and attached with a snap (obviously not gonna work on concrete walls, but that’s a pain for any add on feeder).
I just swept out the mats in the corner and added hay. If it was really crappy hay it would get tossed out but even then it was mostly slung up the side and trailing over, not tracked. It was super easy to clean (unsnap one side, open, fork out hay) comfortable for horses and larger ponies and moved with me to several barns. It’s STILL propped up against a wall in my feed room, I think it’s 30 years old.