The second part of a recent purchase arrived in the mail yesterday so I was finally able to complete the back attachment for my bike. The first part, the beam rack with side frame, arrived a couple of weeks ago and I had been waiting for the actual bag to arrive.
This shows the beam rack with the side frame, that was the first bit that arrived.
This shows the bag that arrived yesterday. The bag slides along the track and clips securely on the front.
The sides expand to form panniers.
The panniers hook on underneath to the frame.
The top of the bag has a pocket on the inside of the lid, ideal for your phone.
The top of the bag can be expanded to add more room.
The top has a handle for carrying and there is also a shoulder strap provided should you want to use that.
The top also has a bungee chord for those items you want to have quick access to.
Now I will be able to fit in those things needed when on a longer trip.
Gippsland Granny 
Looks great. Happy cycling
That looks a substantial arrangement. Not likely to fall off !
Where did you get it from?
Probikekit which is a UK company. Kooby put me on to them. It was quite expensive but it certainly does the job.
Sorry for the delayed response. I haven’t been on WordPress for a while.