I added a cabinet on top of the battery box which is on driver's side just inside the door. It currently has one shelf, but may add another. Then I added a counter using 3/4 inch particle board with Melamine surface, purchased at Home Depot. I added an ABS plastic sink. the cabinet also has a Melamine top and is 4 inches higher than the counter so my Reliance 2.5 gallon water tank with spigot can be used.
I may add an enclosure for the sink and have not decided what to use for a grey water tank -maybe just a bucket for now. I may also run a drain line outside and install a Y valve to drain out or to holding tank.