FROM PEOPLE ON THE NET:
Each entry is all on one paragraph. I’m not fixing ALL their typos!

Undercoating is not a good thing. However rust proofing is. There two completely different things. Undercoating is a tar like product applied to the bottom of a car. Rust proofing is a film like nearly clear product that is statically applied to the end side panels of doors fenders etc. I take the rust proofing and fabric protection. I tell them to forget the under coating and paint sealer.

I worked at a Buick dealership back in the early 90’s. The package that people are talking about is a joke. Let me tell you about the undercoating. We got it in a 55 gallon drum. A green color liquid that I was told to fill a paint sprayer with and spray all exposed areas in the trunk, spray the strut towers and be sure to spray the exhaust. I asked why and was told so the customer smells it and knows we did the job. Now when I was a kid, my father had a 76 Buick Century that he had rust proofed at Ziebart. They drilled holes in the doors and removed the trunk carpet and did a really good job. The car never rusted, we got rid of it when the motor died (Wish I knew how to fix cars back then) The “Paint protection” came in a little bottle called Vesco paint proof, all I did was to wheel it on. The “fabric protector just came in a different spray can, same ‘ol Scotch Guard. Took me maybe 45 minutes to do all three and using less then $50 of supplies. They charged $500 + back in ’92 for all this. I disagree with people that don’t think you need rust proofing, the doors on my ’92 Cavalier are rusted apart. But my ’91 T-bird has just started to rust on the doors. A good quality rust proofing with a written warranty is a good investment.

Properly applied rustproofing with a quality product will extend the life of any vehicle. Stay away from rubberized undercoatings (what the dealer offers) as they dry and chip, letting in moisture. find someone that applies Waxoyl, I have it on two of my classic cars and the frames look like new.

I wouldn’t bother with an undercoat, but taking the vehicle to Krown or whatever the trusted rust proofing company down there is to have it rust proofed once a year is definitely worth the 150$. Up here [CANADA] we have Krown, and by getting it done with them the positives are two-fold. First, if you go every year you will never have to pay more than the first rate you paid. If prices go up, you still pay the same as you did last year. Secondly, if its rust proofed from new and anything starts to corrode its covered under the Krown rust warrantee and they will pay to have it fixed or replaced. It’s a new car, don’t second guess things like this.

Otherwise… for every other car it’s just part of the painting process. So many cars get scraped on the rockers and subframe that paint will come off and rust will still happen. My 91 Toyota Supra I am restoring had no undercoating and I am so lucky that it has not rusted underneath over the past 20 years. First thing I did when I got it home was take off the exhaust and drive shaft, removed the engine and transmission, put the car on a rotisserie, and I ground off all the paint on the underbody and frame. I then used por-15 rust proofing on the whole underbody, inside the subframe,in the wheel wells, and bottom part of the firewall were you can’t see behind the motor. I then applied a good primer on top of the POR-15 I reapplied new seam sealer over all the joints. I then towed the car to the local line-x shop and had them spray the entire underside of the car, and in the wheel wells. It has a nice smooth finish. Is way more durable than any rubberized undercoating and works as an excellent external sound deadener.
I honestly think that the only cars available these days 100% rust proof are the new German cars that go through a rust proofing dip before being painted. So it gets all the internal chambers.

no mater what speed the drill is spinning or what material the bit is made of, avoid like the plague.never let them drill holes in your car. ALL my past experiences with holes cause rust around the holes.And they didn’t charge much because I had the car stripped down on a rotisserie. So it made their job very easy.Once I put the car back together I took it for a drive with no interior carpet or trim and just the line x made my car a lot quieter especially at hwy speeds.