Does it pose a safety hazard trying to get out of your driveway? Perhaps nicely mention that you almost hit a kid on a bike that you couldn't see coming because the RV is blocking the view of the road out of your driveway.
I remember when we bought a new house in a subdivision being built, we were given a list of "subdivision regulations" by the builder. No big satellite dishes, umbrella type clothes lines only, and no trailers parked in the driveway for more than a night (basically, time to pack it or unpack it). Not sure what legal effect those have, or who enforces it, but you might check with your local municipality about whether he is allowed to park it there. I would try nice first though.