Ah, but I don't have EL installed, and I'm fairly certain the version of orbital construction I'm running is the one previous to the EL compatibility update that added ore - I had a warehouse with a load of parts in kerbin orbit, and didn't fancy them being reduced to 1/400th of their original quantity. I'll probably update kethane and orbital construction when I've depleted all my warehouses (or wait till .22 comes out and have a positive orgy of updating things and going "oh no, I've borked KSP"), but till then it's kethane only. That said, it occurred to me that landing a medium warehouse with a mining unit + 3d printer on the bottom, gets you fairly reasonable quantities fairly quickly at around x10 warp - and it's a hell of a lot easier getting spare parts modules from the surface of minmus/mun to orbiting warehouses than it is from kerbin. In the sense that most of my attempts at getting >50t of spareparts into kerbin orbit result in the lifter just falling apart on the pad (I think it's something to do with how heavy the parts are compared to their size on Kerbin, since I can get similar-weighing but 'bigger' payloads into orbit no problem). I might see if using the part cans as mini-warehouses still works though, that's a pretty decent idea for smaller vessels.