Rust Proofing for Canadian Market Prius?

Like most new cars, the Prius is protected against rust by the factory. In the New Car Features book for the fourth-generation Prius (NM3200U, available by subscription to techinfo.toyota.com), Toyota writes:

Rust-resistance performance is enhanced [by] extensive use of anti-corrosion sheet steel, as well as by an anti-corrosion treatment that includes the application of anti-rust wax, sealer and anti-chipping paint to easily corroded parts such as the rocker panels.​

Toyota Canada’s New Vehicle Warranty & Coverage page has links to their Owner’s Manual Supplement books with the detailed warranty terms, including a five-year warranty against corrosion perforation.

I don’t know if your salesperson’s comments are correct, but considering that rust-proofing treatments and devices are very profitable for dealers, if he said they won’t sell you one, there is probably a good reason.

An article on wheels.ca and a posting on toyotanation.com quote written responses from Toyota Canada to similar questions. There seem to be several concerns, including that an aftermarket spray-on treatment might hide or damage the bright orange insulation on the high-voltage cables. So-called electronic rust inhibitor devices—if they are effective at all, which seems to be in question—could also cause problems; as the spokesperson quoted in the first article said, “Any form of electrostatic charge induced through the ground side may affect and shut down the hybrid system.”

 

A testimony to how rust resistant the Prius is, SWMBO's Gen 2 is now 11 years old with no rust (apart from the surface rust on the suspension components underneath), it's left outside, not garaged and here in the UK the authorities chuck salt and grit on the roads throughout the winter every year.

 

If you look I think you will find the brake and fuel lines are -inside- the chassis (in a trough covered by the undertrays). I'm betting your 3rd gen wouldn't have rusted even if you didn't purchase the rust proofing. Mine shows no sign of rust. It's kept in a garage, but that is worse than leaving it outside (rusting temps happen for longer periods in the insulated but unheated garage and the humidity is trapped inside).