So I hear your concern, but in the years I’ve had to pull a board before taking the cart out, this has all been an issue zero times. It’s not like the board is so wedged in there that it’s challenging to remove; you literally just bend over, close your hand over it, and pick it up. Yeah, from time to time a horse does manage to land a pile on it, but it’s not like that’s the full width of the board, or that the entire thing is buried under manure. I kick off the poop, or use a shovel to give it a little scrape off in being fancy, and pick it up. Raining has never been a deal, I guess it does get wet if rain is blowing in? And it’s never once been frozen.
I’m not trying to talk you into doing something you don’t want to do
But I do think you’re picturing the set up as far more complicated than I’ve certainly ever found it.
I find the cost of these horse specific floor brushes just bonkers for something that can be accomplished with some scrap wood probably nearly every farm has lying around. Or repurpose a door sweep:
https://www.tmhardware.com/Door-Sweep-Aluminum-with-4-Angled-Brush.html
Which is still kind of $ but less without the “it’s a horse thing!” branding.
Garage door bumpers are also kinda interesting for this use, I wonder if they come tall enough to be useful?
https://www.tmhardware.com/Garage-Overhead-Door-Bottom-Seal-1-438-W-Aluminum-Track-with-1-25-H-Neoprene-Compression-Seal.html