I think we might need to more clearly know where you are at in the project.
Glued up? fretted? In pieces?
Large boxes can be cool, but create their own challenges too. One tactic is to locate the bridge pretty far up the box, but even then you will likely incur some limited access to the higher frets.
This kind of thing is why I ALWAYS suggest at least a sketch, preferably a reasonably accurate scale drawing mock up before proceeding to build. It can save you from many potential headaches.