The size of it is supposedly L32CM*W17CM*D11CM as per the eBay listing.
I was also thinking of
something like this. Since it has a plastic mount already on it, mounting it further away from the seat and legs could be possible, avoiding the need to build a completely separate rack. It's also much cheaper at just 6 USD, so not a huge loss if something happens to it.
Has anyone had experience with plastic connections in general? Do they tend to break? I was also looking at a smaller bag that I could use for quick rides to the shop etc., one that would easily just pop in and out of the connector.