Good news; you can have extra storage in your trailer box. Bad news; you gotta make it yourself (if you want one like the one pictured below). I bet you could substitute a canvas shoe holder from Bed, Bath, and Beyond for your storage needs. Just be sure to use 3/4 inch - #8 or larger maching screws and washers. You should afix the pouch on the top and bottom.

Hey! Thats a great idea!

I used shoe pockets in my pop ups. Inside tho. They just folded up like all the other fabric when it came to closing time.