While we’re on the subject, I’d like to post a few pictures. I built Coroplast panniers in 2015 and 2020. The 2015 version survives on another bike. But I learned a thing or two, this concerns the cutout for the anti-heel-strike.
New panniers, 2020
2015 panniers
2020 left, 2015 right
NOT a complete diagram. Panniers are 19 and a half inches wide by 12 inches deep, by 24 inches long. Home builders should base there center line on the width of their bikes own rack.