Thats the sort of size I was thinking. Bed still pulls out, space on floor for dog when other buddy seat is removed. Something more rounded though, half a semi-circle or triangular.Here's a pic of my cheap and cheerful option. I made it out of 18mm ply so it's a bit heavy. No water plumbed in but plenty of space to store a big bottle underneath.
I would like to see a solution using the existing brackets. T: