I have some white vinyl cling film I'm going to try. I'm not sure if that's the white film you see on new cars that are being transported on car haulers, but it might be. The thickness is something along the lines of Contact paper, but it sticks by "cling" and not by adhesive. I'll report back on how it works. I've seen a commercial product called "Road Wrap," but have not tried it.
For a one-time long haul, someone [and I can't remember who, but it's someone like Pettit or Interlux] makes a spray-on coating (I once used it on a large trawler being prepped for a cross-country haul). But it wasn't something you'd put on casually. I've seen boats shrink-wrapped for the same purpose.
I've heard of people putting on a thick coat of wax (and not buffing it off), but I worry that it would be baked on/like "concrete" days or weeks later when it was time to take it off (have never tried it though).