It looks like maybe a couple of binders could fit on the end? Maybe a good way to keep the maps from moving.
I thought I'd share my counter storage idea in case it is of use to other player.
This storage boxes are made by The Really Useful Box company and this is a wide low one with a capacity of 9 litres. You can get it in blue as well. Rather serendiptiously they hold exactly 10 GMT counter storage trays, 2 side by side and 5 deep. The lid (which clips on)neatly touches the top of them so they are not loose inside but also don't press down on the trays. They couldn't have been better designed for teh GMT trays.
The GMT trays enable you to see what's inside and easily find your counters.
I've looking for some time for a box to store the maps in without having to fold them and low and behold I was in an Office World shop (zzzzz) the other day and found this....
The maps fit so well width ways there is about a centre or less to spare.
These may not be everyones choice but it's another option.