I plan to use the battery compartment for the lithiums, and will likely need to make another compartment - that's why I'm looking at a flatbed, for the extra utility space.
Toilet, I would be more concerned if other people would be using this, but since it will be only me I think the composted will keep up. However, I am thinking about this carefully.
Desiccation: Off hand I'm not sure how one would keep up with daily waste accumulation. The cow pies of the west were air & sun drying for likely long times with the settlers gathering them as they needed... no?