The PortaBote people might not have seen your message. It's show season
and they seem to be a small shop.
It's funny, though. Our older PortaBote has plywood seats. The plastic
ones seemed to be an upgrade, but obviously they need a little more
engineering. Truth be told, the plywood seats could have used a bit more
as well.
Wouldn't be surprised if your communication induced a few changes,
though. Few have used one as much as you have.