for a run in.
Basically...I have a long, narrow (think road) type of area along an exterior fenceline of a pasture, but on the interior (not public road) of the property. I'm considering having it graded, and useable, and then putting up a 'shed roof' narrow, but tall... structure over it for : hay storage/ boat or trailer storage, etc) that you could still drive thru on one side with an atv or lawn mower for access even when items where stored.
Now. Because this is along an existing fenceline...I got the idea of: setting 'wall' of this (of course with kick boards up high enough) just on the INSIDE of the fenceline...and having say, a 4 ft? overhang roof on that side...and make it like a covered hay feeding station on the horsey side. What I'm brainstorming is: a way to drop hay into a slow feeder type of idea from the 'storage' side. I'm envisioning: maybe a vertical type of mesh screen on the horse side, (think 'window' but barred/mesh) and on the inside of the shed area, just place? the slanted hay feeder idea, so the hay continues to slide down toward mesh screen window as horse consumes?
Trying to figure the best way to utilize this structure on the horse side of the fence, make it safe, and this came to mind! (yes, I could extend it out far enough for a run in as well...but I have that option in the other field, and this I can see as a way to keep hay dry/off ground and available when I use this area) no electricity here, and just easier to utilize this as a hay feeder area vs. full run in.
"Indecision may or may not be my problem"
Not quite like your potential set-up, but my run-in has a long (10 foot?) hay rack that we made out of horse panel (very thick grid, 2"x4" openings). It's just angled out from the wall so the hay goes down like a normal hay rack. They eat fine - but slow - out of it. Now that I have it, I think even 4" x 4" would work but paranoid me likes the fact that they can't get their little footies through a 2"x4" grid. What you're describing sounds like it would work great.