RE: New Fluence owner - rust never sleeps...
Cars really don't need corrosion protection now. A wax layer is more likely to aggravate trapped water/corrosion than prevent it.
Sheet metals in cars are now typically zinc treated before manufacture (not quite 'galvanized' but still a sacrificial zinc layer) so the key is to just keep an eye out for any dings that might have exposed the under layers as you will want to get that covered asap. But so long as you do do that, then the corrosion will be halted as the zinc will be passively sacrificed (unlike bygone days when the steel would then just carry on corroding under the new paint).
This is why the corrosion warranties are now very long, but so long as you take it for routine inspections.
Weld points can still be a problem because the joining process will degrade or remove the sacrificial zinc, which also applies to pressed/stretched parts ('stressed-steel') areas that will gain structural strength by mechanical working but may damage the zinc cathodic protection . This is usually managed these days, just a few design flaws might escape into production (e.g. the front suspension turrets on the older 210 E-class).
Don't use tap water to wash cars in, it is full of ionic contaminants that aggravate corrosion processes if they have started. Install a water butt to collect rain and use that.