My 2004 Prius has 121,000 miles in CT - NO RUST even though there are some scratches to bare metal. Some of the panels seem to be aluminum. JeffD
Most all cars manufactured today are primed w cathodic ELPO. Also large number of vehicle panels are made of "special" metals (ie: zinc coated steel, aluminum, aluminized steel, plastics (I know they are not metals), etc.). These and the cathodic ELPO have proved to be very effective in preventing corrosion. Back in the 1970's the average no perforation life of a fender in the N.E. United States was 3 years and that for a rocker panel (remember those) was less than 2 years. Today you see very few cars on the road that start to look bad at even 15 years of age, assuming they haven't had crash damage repaired and repainted. Toyota was one of the leaders in these changes 30-35 years ago.
My car is too new to show any effects from salty winter driving - but seems like the all of the plastic around the wheel wells, including plastic bumpers and rear panels, should keep some of the potential rust to a minimum.
There's a little rust around some of the exhaust system on my '04, but it doesn't seem to be advancing. There's also a little corrosion on some of the bolts that poke through the body shell to the outside, but some of the important ones of these [ground points, etc] I've pulled and anti-seized. There's also a little rust coloration, but no real degeneration, on some spots where the black paint has flaked off the suspension parts. The body itself is still pretty much pristine, from what I can tell. On an '04, which is kinda impressive. . _H*
No rust from the road treatments in NO VA. I think they were trying a new mixture this year and it isn't as corrosive as salt.
I kept my Prius 5 years. I was pretty anal about hosing off the undercarriage, especially the rear wheel wells at the bottom arch, that flat spot where dirt/sand appears to collect I also liberally applied Fluid Film over all the exposed metal. Manufacturers always claim to have cured rust. But if you live in an area with road salt application, it's pretty apparent that although they're getting better, after 5-7 years the rusting starts
In Milwaukee, salt flies as fast as the snow, and I haven't seen any problem so far (although I've only been through two winters with the Prius now). My wife's 2006 Corolla still looks fine, assuming the two vehicles share the same metal treatment from the factory. Relax, Ford holds the patent on rust! Jim
6 salty & sandy winters in Minnesota. No big deal. The only visual evidence of aging is some rust on the rear brake drums. That's it. .
I have rust 2007 29k mile always washed and waxed. rust is coming through low on fenders, doors, and left rear quarter panel. small dots of rust, at first I thought it was a stain, but its under the clearcoat, although one dot has broken through the clear coat. I will be calling the dealer this week. something happened when this was factory painted, I am not happy.
I realize you have a low post count, but would love to see photos of this. A problem with surface prep will cause the condition you described. If it was perforation rust, you could easily poke your finger through the metal