Whenever a replacement panel which is a part of a box section has to be welded into position, the opportunity should be taken to give as much protection first to the side which will end up inside the section. Obviously, the area of metal which is to be the actual join will have to be cleaned bright and de-greased, but most of the panel can be treated to several layers of primer. Some of this paint protection will probably burn off during the welding process, but any protection is better than none.The maximum protection against rusting will be gained by using one of the better 'rust arresting' primers rather than normal primer. In the author's experience, the rust-arresting primer previously mentioned also performs very well on clean metal; better, in fact, than normal primers.The Beetle has a number of box sections, most of which can (and usually do) rust from the inside. When a panel or panels from a box section is repaired the opportunity to give further protection to the metal should not be missed. As soon as the welding is finished and the metal has cooled, a wax-based product such as Dinitrol 3125 should be applied. This will often entail drilling a % in. hole in order to gain access to the enclosed section, and the hole should afterwards be sealed with a rubber grommet.The wax is applied either with one of the hand pumps supplied by the manufacturer or via a compressor-driven 'paraffin' or underseal spray gun. When cold, most wax-based products are of too thick a consistency to spray properly, and so they should be warmed until they become thin enough by standing the tin in a bowl of hot water. A cheap though less effective alternative to wax is old sump oil, which will have to be thinned in order to get a fine spray and to which some people add a little creosote.Underneath the car, not only the bodywork but also items from the suspension benefit from protection against corrosion. There are various ways in which the suspension and associated components may be protected.If the underside of the car is steam cleaned, then components previously covered in a layer of mud will be revealed to possess a covering of rust underneath. It is not always practical to clean and re-paint such components nor to partially clean and then use a proprietary rust arrester. Many people slow the corrosive process in such cases by painting on old engine oil.When oil is applied to a ferrous surface, it spreads to form a thin protective layer which offers the considerable advantage of remaining 'self healing' for a period of time—that is, as if the layer is breached by ascratch then the oil will again spread to re-cover it as long as it remains thin enough to do so. In time, the oil not only thickens of its own accord but also because it is absorbed by dirt, so that in order to work consistently the process should be repeated from time to time. If oil is used thus then be very careful not to let any come into contact with the brakes.Proprietary wax products such as Dinitrol 3125 are used by many in place of oil (which can be very messy to apply), mainly in the protection of the underbody. Waxes remain reasonably fluid during the summer months and so can be self-healing, but in colder winter climates this will not happen.Underseal is the usual product utilised for underbody protection. It is a very thick substance which can go some way towards absorbing the impact of stones kicked up by the road wheels which would otherwise expose bare metal to the elements. Underseal forms a thick and hard 'skin' over the metal, and here lies its greatest drawback. Any rust which exists before the application of underseal or rust which forms afterwards can spread rapidly and virtually unopposed, unseen under the surface of the underseal.Underseal works best on new panels which already have some form of rust protection, and is best considered a form of protection for the actual anti-rust protection.