Where ever you put them, ensure they are mechanically secured, and that the mechanism is robust enough to handle the load. If they bounce/slide around in rough seas they can cause a lot of damage. This goes for anything stored in the bilge like a spare anchor, shaft, bbq, or anything else. Smaller items like spare oil, parts, etc. should be in secured containers with locking lids. For the smaller items, I like using battery boxes. They're easy to secure and are vented. Some of the things I've seen unsecured in bilges are pretty scary when you think of what could go wrong. The most common are ropes, spare running gear, anchors, outboards, bbqs, and portable fuel containers full of fuel