Maintenance while on the road-best places?

I've done wiring and extensive brake work (while jacked up) by necessity on the road.  Larger parking areas where there's no traffic are best.  Industrial lots, mall lots near auto parts stores, even a church lot where we happened to see someone and ask permission at the right time.
I've seen a few self serve auto/truck wash bays (huge) that accommodate campers, and used one.  Just be very cautious where you direct a power spray as I consider the gaskets and caulking on these campers to be relatively fragile.  Rinsing off heavy dirt road  debris is fine.  The underside is not sealed from water intrusion and there are open AC and other floor penetrations.