Can I use rust removers and paint coatings to protect a rusted vehicle underside?

The difficulty with these jobs is that the process of preparation is extremely time-consuming when using any kind of normal coatings to treat corrosion or even rust converter.  For example, to use Deox-Gel you must remove all loose coatings and corrosion, apply the gel and leave it working for around six hours then scrub with a stiff-bristled brush and water, if corrosion remains, reapply and repeat until the corrosion is gone. Very messy indeed when laying on your back, however after this, Electrox can be used to good effect. You could reduce the amount of preparation time by using Hydrate-80 or powered wire brush would be needed which is perhaps not feasible on a driveway.    

A better method…

After a thorough cleaning of the underside with a steam cleaner or pressure washer (Surfex-HD can be used for better cleaning in conjunction with a pressure washer), you will need to remove any loose coatings or rust where possible. Remove any wheel arch liners and covers and thoroughly clean these areas too. Then, use Dynax-S50 to inject wax into any box sections (these are always the worst areas) and also use it behind the wheel arch liners. You will need around four aerosols. Then on the open areas, suspension assemblies etc, use Dynax-UB. These products will provide excellent protection to steel irrespective of whether they are corroded or not. They’re simple to use and will make the job an easy one. To attempt to use paint type coatings would require huge amounts of time. The exterior wax treated surfaces, where exposed, should be examined on a yearly basis and topped up as the waxes can be worn, for example by tyre discharge. The cavities can be left for 5 – 10 years without top-up. I also suggest that every two years the wheel arch liners are removed so that you can clean away any debris, this is important as mud will act as a poultice if it builds up excessively.