That's a pretty cleaver idea, and a definitely an idea to add a space saver in an RV. Hanging space savers under the cabinets or shelves is a great way to utilize empty space. In my previous camper I hung some stacking wire shelves, turned upside down and secured under this corner shelf, and also did one in the living room area.
The hinged box is a cleaver idea too. It could come in handy storing important papers, remotes to the television, video or audio CD's or any number of things, provided you've got an old hinged box laying around you don't need for anything any more.
Here's what I did. You can see the wire shelf under the corner shelf where the television was originally suppose to sit before attaching to the wall instead. We don't have this camper any more, and our current one has plenty of storage space, so don't need anything like this now:
