800 population and 1600 are low counts. Aside from car counts, you have to ask where that population is going. I’m not sure if people on their way to or from camping or hiking are interested in cleaning their car that close to the site. If it were me, I’d wash when I get home, you’re only going to pick up more grime on the rest of your trip back. Also, people in that scenario might be more inclined to use a self serve wash to clean off camping equipment, coolers, boots etc. and maybe get a layer of dirt off their car - maybe under wheel wells and in hard to reach areas etc. Not sure how dirty the cars get or your road condition. It is not a scenario that I would build any wash, but IMHO if you had to build something, I’d say a self serve would be more useful to the demographic and a smaller investment, but it is still a dreadfully low count to build anything.