OP here. WOW, this thread was from like three years ago.
I never did end up making my slow hay feeder. I have the hockey nets and all the clips and everything, just never did put it up. The MIL decided against it at the time but it now in the process of making a different style for her piggy mare.
I absolutely LOVE the slow hay feeder concept. Whenever I have my own place, I'll definitely be implementing this concept there... makes so much sense.