My whole van is my privacy area - never heard of blinds and curtains?. With a porta potti and a sink I have the same facilities as most bigger vans do. Fine for wilding in between visits to sites to empty grey & black waste and fill up the water, like most bigger vans. The best bit is that I can go further for the same fuel money and as Rob says I can go down country lanes that you couldn't take a big van down. I can go under most height battiers too, for daytime parking.
Human waste being left in the countryside has nothing to do with it - any cases I've heard about have been either due to walkers who are too far away from a public facility and get caught short, or from motorhomers dumping their black waste.