Welding looks impossible to me without removing the foam etc. from the area. Welding involves a lot of heat.
I agree with Oasisbob that this probably isn't aluminum, at least gauging from the picture; it looks more like painted steel. Pictures can be deceiving, though. Aluminum doesn't rust, has a somewhat shiny gray surface, and is comparatively soft (many alloys can be cut or marred with woodworking tools). Welding aluminum is rather tricky work, I gather both because it is hard to keep clean (it oxidizes quite quickly on the surface) and because it has a very narrow plastic range between not joining together and forming a puddle of molten metal. I have absolutely no experience myself welding anything, though.
I might try a reinforcing plate and some JB-Weld (and mechanical fasteners). If there's any easy way to do so, I'd also inspect the same joint on the other side for the same problem.
