this is not true, the por-15 metal prep self etches and leaves a zing phopshate coating that allows you to paint even new metal. i've used it on new trailer hitches, sliders and skids and it is extremely durable, it cures to a hard epoxy like finish.

por-15 is a 3 step process: degrease (they make a degreaser or use whatever you prefer), metal prep, and then paint

I live in utah and snowboard a ton, plus my 4runner came from upstate NY with a ton of underbody rust at a really good price with under 100k on a 2011. Problem was the previous owner tried to cover it up with that ziebart crap... never put that gunk on your car. It trapped moisture behind it and my car started rusting from the inside out with that gunk I couldn't peel off...
So, I had to go to a body shop and have the whole underside of my 4runner sandblasted, rust proofed and then undecorated... pain in the penis. The shop I took it to was more than fair, guaranteed their work and said I saved the vehicle. I have to find out what rust proofing they used, but I guess time will tell.
Having to go through this ordeal, where the 1st undercoating shop wouldn't touch my 4runner because of all that crap that was coating it, and the fact that toyotas tend to rust out. I think I will be undercoating all my future cars.

Meh, I used to spray my GMC frame with FF and it definitely does come off. The first hard spray through a car wash will take out a lot of it. It's great for farm equipment that doesn't go through the car wash though. This time aroun I'm going to give the CRC marine rust inhibitor a go. It dries much like LPS3.

You are correct- you have to use the metal prep on a new finish, but Paint Over Rust is the original idea. It works great, just don't get it on your skin.

Pretty good video on the subject
YouTube

Bumping this as didn't want to start a new thread, but my question is, is rust-proofing and underbody coating needed if you wash your vehicle frequently (including underbody spray), like say once a week?

Another question, but if I have this done at a shop, should I have them remove the skid plates and spare tire to hit those areas as well? Like would they be able to do that? I don't want to do it myself because it's freezing out here now plus I don't trust myself not to mess something up and not be able to get them back on or something.

my trd orp is 3 years old. I took the lift off this weekend and there is a ridiculous amount of seized bolts and rust starting everywhere already. Granted, I have 80k on my truck, most of which was done in 2 years, and that has included a lot of driving across the west to go skiing, but i'm really wishing I had coated it with something.

Absolutely yes. And also have them coat the entire trailer hitch.

I've lived in the rust belt for my entire life. Trust me, washing a vehicle regularly helps, but there is no substitute for additional rust proofing. As for what "proper" rust proofing involves, here's what I did:

Complete Corrosion Protection for my New T4R | Tacoma World

BTW, I would never use conventional "rubberized" undercoating to rustproof any vehicle - particularly Ziebart. It causes more problems than is solves.

What I did after watching Repair Geek, I went with Fluid Film inside the frame and Blaster Surface Shield every where else. Repair Geek video on YouTube is impressive for rust prevention.

Do whatever you can. Its impossible to get 100% of the vehicle, but anything is better than nothing. fluid film, wd40, woolwax, etc etc. Wash when you can. Im also a big fan of rough sand, clean and rustoleum rust converter when you see any

This is absolutely spot on! After losing my beloved 4th gen V8 to frame rust that I lost control of, I fluid film my 2016 every year. I used to have a shop do it, but he's so busy, he won't do it while I wait any more. So, for the past three years, I just buy 6 cans at Lowe's, and do it myself. Drop the front skid, and the spare, and just do the best I can. contrary to what's been said, it holds up for "most" of the year. I'll touch up areas when I do oil changes throughout the year, but for the most part, once per year is enough, even here in Jersey where towns and counties seem to have contests on who can use the most salt on the roads.

Never undercoated any vehicle I've owned and it's never been a problem (also never owned a Toyota, just a couple Fords and a couple Nissans over the past 30 years...).

Guess I've got time to figure out what I want to do since I won't have my 4R in the next 2 months (according to what my sales guy can see coming)...

The issue I've read with Fluid Film is that it attracts a bunch of dirt and grime and makes the undercarriage look filthy, is this true? And also that if you wash the vehicle frequently with an underbody blast, it washes off too easily.

The 4th Gens from what I understand, Toyota made a blooper and did not properly coat the frame with rust inhibitor and thus the 4th Gens became known for rusting if you weren't careful.