A former employer of mine did some research on this. We found that the two part epoxy adhesives were actually stronger than the parent metal. Using them produced results similar to welding as far as trensile strength vs the parent metal, that is the material tore before the seams did. However, because much of this technology is new and long, long term impacts are not understood, we never used it to replace structural welding. A big part of that is because we had contractual obligations to provide product that met AWS standards, which are widely understood, but there is no similar organization of standards and regulations regarding adhesives that everyone is willing to agree upon.
Would I use it on body panels, sure, but you need to have lap seams to successfully use it as it will not have the strength to use on butt joints. These lap joints would be visiable on one side and are a point of debris collection (ie rust starters) if left in exposed areas.
