I'm now in a position where I'm ready to hang my Seleco projector - but I've hit a minor problem. My plasterboard ceiling has a 12" cavity above it. Above that is concrete. My plan is to get some long (15" - 18") masonry bolts which will anchor in the concrete, pass through the cavity and plasterboard enabling me to hang the projector bracket. The problem is getting hold of such long bolts. I've only tried screwfix and my local DIY store do far. Anybody know where I can source some?? Any alternative mounting suggestions? Cheers, Ben.