Small top box for a 2015 Glee

[mrp192]

My 2015 Glee has the standard Hepco & Becker luggage with the top box plate attached to the standard rack.
I want to try and find a waterproof smaller top box that would fit to my top box plate, just big enough to take an A4 size folder, and not very tall, maybe 100-150mm.
The only things I can find online are very small or quite large softbags and large top boxes.
I’ve tried the H&B website but they don’t list anything similar.
Has anyone found something they could recommend?
Thanks.

[hotbulb]

I'm not aware of anything specifically designed as a bike accessory that fits your requirements. You my be better off looking at waterproof (document?) cases such as the Pelicase range (£££)