If you need to use the inside maps when you are running the module, you can stick each half inside a fold-out two-page sheet protector, and stand it on end like a
DM screen. You can add backing boards if it's not sturdy enough to stand on its own. I've made DIY
DM screens this way, including sticking maps on the inside on occasion.
Like this, but take it out of the binder and stand it on end.

Zenopus Archives
website &
blog: Exploring the Underworld of Holmes Basic D&D.
Holmes Ref: Reference Sheets for Holmes Basic Referees, also compatible with OD&D plus the Greyhawk supplement