In metal forming or metal bashing there is a technique called dishing into a sandbag. Here the meaning of the verb is to make something into the form of a dish (the shape of a piece sliced from a hollow sphere) and in particular by hammering a metal sheet into a sandbag. Any ideas - car body repair shops should be familiar with the process and I suspect there are differing translations in different countries. The mexican translation would be fine for me. If it weren't for the stay inside instructions, I could just go down the street to a nearby bodyshop and ask.