There you have it, your own shower.
I took a slightly easier route, although it is dependent on space in your vehicle! I brought a pump action shower, just fill with warm water and off you go.
The pump action shower is basically like one of those weedkiller applicators, a big water carrier which you pressurise by pumping a handle and it sprays out water for long enough to have a shower. It worked suprisingly well, in fact better than expected!