Do they use salt in Colorado, Denver specifically? My daughter is going to move there after graduation with a pristine, Houston all its life, 2006 4Runner sport. We both hope/plan for this to be her daily driver for another 10 years. Wondering if we should be concerned or take some preventive action...

Even if they don't use salt, it'll rust, just not necessarily as fast. And if sometime during that time period they (God forbid) start using brine...good luck. You'd probably be best off taking preventative measures anyways, I have heard tons of really great things about Fluid Film.

Is this a DIY product? Doesn't seem like it would be a lot of fun crawling underneath and spraying this stuff all over, including on me and the garage floor. And how would it get into the frame if it doesn't have access points to spray into?

Salt and Magnesium Chloride and gravel. Don't worry, vehicles don't rust in Denver or Colorado as a whole. Car washes are rarely closed for more than a week due to below freezing weather so one is able to spray off accumulated grime, put the wand on the underside, wheelwells, blast the skid plate.

The 2008 was a CO vehicle all its life when I bought it and even though the frame was packed with Western Slope silt, it wasn't rusted at all. The thing is the air is perpetually dry here year round, it's a semi-arid climate. Dry climate means even with accumulated dirt it doesn't STAY damp.

The gravel blasts the paint pretty good, like on the rear axle. Just keep it clean.

Really only thorough washing is needed in CO. There will be surface rust where paint is gone on the frame and undercarriage, but not the godawful things I've seen from east of the Missouri River. The air is just too dry here, it sucks the moisture out of accumulated dirt like I found in the 2008's frame when I bought it.

Salt itself is minimally corrosive unless it is WET. A dry environment like CO, vehicles are constantly DRY, unlike a humid environment.

Anyway, I still haven't figured out how the 2008's frame got packed like it was. It literally was packed with silt to the side holes on the frame. That's how I discovered it, ripping the XREAS off to put a BOSS suspension on it. Frame wasn't rusted though.

I did spray FluidFilm on the 2008 after I flushed the interior of the frame rails. Probably wasn't necessary but it was on jackstands installing the new suspension, so I did it. Spray cans, sprayed it into all of the openings I could find on the rails. It's a waxy product, lasts maybe a year on exposed surfaces. The product has great reviews.

Your daughter's 2006 will be fine without such treatments. Frames don't rust out in CO, I've had Tacomas, a Tundra, notorious rusters in Eastern humid climates, no problems here.

We moved from CA to MN for almost five yrs with a 2008 in 2010. That part of the country uses salt religiously and it’s on the ground intermittently 6-8 months out of the year. Knowing we’d eventually be moving back to CA I was super concerned about rust and did a ton of research on options, including undercoating, ultimately deciding on regular car washes because the undercoating processes can miss areas, certainly including inside surfaces of the box frame.

Did a bunch of research on good full-service car washes in the area (undercarriage wash was a must), picked one not super close to home but with stellar reviews, bought an unlimited-visit monthly membership and went at least once weekly during winter months. We moved back to CA 5 yrs later almost entirely unscathed.

Just my experience moving from no-worry to high-worry rust environments.

It's a long shot, but I'd happily take a fat buyback towards a new Toyota truck.

https://www.forbes.com/sites/jensen/.../#685131aa7302

Like @flipflopnfly says it's the magnesium chloride that is the killer of all things metal. It is mostly applied as a liquid, some call it brine, but it will eat through painted and primed metal. It turns semi truck trailers to scrap metal in a few years.
Even here in Oklahoma where we don't get much winter, cities have started "pre-treating" the bridges if winter weather is forecast. I think governments are being sold this "new" form of road deicing by some very unscrupulousness business people.
Don't just take my word on this, read up about magnesium chloride and metal. Talk to an automotive or other equipment manufactures. We need to petition to stop using the stuff on our roads.

you are 100% correct. The chemicals being used are politically motivated business practice. They need to go back to sand! The rate at which these chemicals cause corrosion of vehicles and roads which together compound the problems 10 fold. Not to mention, the most likely long term effects on the environment and our health. Seriously need to start a petition.

Funny, none of my older cars like my 1996 Honda Civic has any issues with rust driving in salty snowy conditions its whole life.

You're 100% on point. Even worse than the MC is the brine IMO. Horrible stuff. Petitions do not do jack shit though. The people signing it will be a minority. Most people go through a car every ten years MAX, not enough time to understand the effects of these chemicals for some average joe shmoe.

Dang, I have a 2007. It'd be nice to get the frame taken care of. I got the rust ground off it and an undercoating put on it so hopefully that will alleviate most of the potential rust problems.

Unfortunately, even though the exterior may look good, a lot of the corrosion problems we have originate from the inside of the frame where it’s very difficult, or impossible to clean/coat correctly. I do agree though, that something done is better than nothing. I sandblasted, primed and painted my frame, but I’m still very worried about what’s happening on the inside where I couldn’t get to.

You'll see a tanker truck spraying scalding hot water/mag chloride brine before every blizzard here. It's nicely aerosolized so at highway speed it gets inhaled into every nook and cranny of your vehicle, especially if you pass the truck and get a "broadside" from the sprayers.

Go to an underbody car wash as much as possible in the winter, if you let that shit sit caked on your truck for a week it'll start to cause mischief.

And the truck in the story looks like it spends its weekends in half a foot of saltwater at a boat launch... never trust anyone named "Gary."