[Espeefan]

I'm curious about this as well. I'm subscribing to see what I can learn, but I to would think some type of epoxy would be your best bet. If not that, perhaps you can add styrene ribs, internally, to the styrene pieces you want to attach to the metal portion of the tank, and simply drill holes through the metal, and then run a self tapping screw into the styrene rib. That way it would also be removable, in case you want to make repairs, or paint the part separately.