I am just getting into the DIY rust proofing game myself. I am evaluating several different rust proofing compounds and will be gathering data over the next few weeks, months, and years. I am not interested in paying someone to do carwell or krown, nor are any of those treatments available in my area. I am focused on the do it yourself chemcials and their equipment only at this point.
So far I rust proofed my 2011 siverado with Corrosion X Heavy Duty by spraying it in with 6 spray cans and then using a paint brush to spread it around evenly. It dried to a greasy/waxy coating which is really thick. It as been 4 weeks now and really seems durable. It does collect some dirt but it doesn't hold the dirt real firm and you can use gentle garden hose water pressure to rinse the dirt out of the corrosion x without thinning or removing the corrosion x at all. I am not sure if this is a bad thing or not but I have to say it. Corrosion X HD did seem to soften the factory rubbery/waxy undercoating that came with my truck. The areas of it that were already damaged from rock impacts or whatever have now softened, curled up and fell away from the frame, leaving the corrosion X HD coating but bare metal underneath. The un-damaged area of the factory coating are still perfect with the corrosion X HD sitting pretty on top. Now, I am guessing the softening/falling off process would have happened over time without the corrosion X HD anyways so I am not upset but this may really anger some folks who try it. Fluid film says it also may sofetn some types of undercoats so this may just be par for the course with any type of rust proofing spray. The only real down side I can see with Corrosion X HD is that it is very expensive, Over $100 a gallon bulk or 14$ + shipping for a 12oz areosol can.
My 2002 pontiac sunfire was rust proofed with non areosol fluid film (Fluid Film NAS) using a latex paint spray gun. The spray gun I bought worked perfectly and the application process was perfect. I used the gun to shoot everything and then went back and used their aerosol can attachment to spray inside all the voids and access holes I could find. I did not drill any holes, I just used every space I could find. the process cos me 3 cans of areosol and about 1/3 of a gallon of the bulk NAS formula. The process took me about 4 hours and gave my 30 gallon compressor a bit of a workout. I let my car sit for 24 hours and then drove normally. The fluid film creeped into every litte nook and cranny and got inver everything everywhere you could imagine on the car! It even quieted down my squeeky suspension and seemed to soften existing rust I had. I was really loving fluid film up till this point. Now the bad news... the bulk fluid film I sprayed (a pretty thick coat at that) in and around the wheel wells was 100% gone after driving only 20 minutes in a rain storm. The rest of the car held up pretty well but it collected alot of dirt. It has now been 2 weeks and the fluid film is holding up just OK. The underbelly of the car is still coated well with fluid film (and dirt) but basically any area of the undercarriage that is in reach of the wheel well wash, is dry. At this point, I can't see how fluid film could possibly survive a winter in the rust belt. Fluid film works really well inside the cavities of your car but frankly I am not so sure it is durable enough to be used as an undercoat/rust proof. I really want to like fluid film because it is non toxic, inexpensive $45/gallon bulk (with free shipping) and very versatile but the durability does not look good enough for me.
To give fluid film a fair shake, I just ordered the heavy duty thick film (grease) version of fluid film called fluid film AR. It is not recommended as an undercoat because it is difficult to apply (brush only) and really takes the convience of a sprayer away but it is supposed to be much more durable than the NAS fluid film. My plan is to just paint on the fluid film AR in the high wash areas and see how it does. I have also seen people melt the fluid film AR by putting it in a wax candle melter and then spray it with a spray gun while it is still hot and liquid, I may give that a try as well. I need more time to check out fluid film AR but in the mean time, I can't recommend fluid film as a vehicle rust proof at this point, it simply isn't durable enough. If you really want to use fluid film as an undercoat, it will need to be touched up quarterly at least...... YMMV
Finally, I just received a shipment of 6 cans of Amsoil Heavy Duty Metal Protector for testing as an undercoat/rust proof. I will be treating my father's 2002 jeep wrangler with it and I will report back when I do. At this point, its advantages seem to be a reasonble price $8.20 + shipping (that is without the dealer/prefered customer pricing) for a 16 oz can and the fact that it is more of dry, waxy film which should (hopefully anyway) not rinse away so easily and collect less dirt than fluid film. The biggest downside I see with the amsoil is that it is not available in a bulk form and is more toxic and less versatile than fluid film. Stand by for more data from me on amsoil.
Sorry for the long post but I wanted to share my DIY rust proofing data/opinions that I have gathered at this point. I am sure someone can benefit from it. Post up if you have any questions or input.
