Something you might want to research is tiny houses - whether you go that route or adapt some of the ideas to RV living. One idea you might be particularly interested in is a composting toilet which allows you to avoid blackwater (you can go as cheap as a bucket and sawdust to ones that apply some electricity to speed up the process and vent to the outside). There are loads of videos on youtube about tiny houses (in which composting toilets of various sorts are frequently featured).