So, I'm a bug proponent of the idea that to give yourself the best chance of rescue when lost at sea, you really want to have multiple signalling devices. While PLB's are perhaps the most important, they can fail, become damaged, etc. A "last mile" solution such as a signalling mirror, dye packet, chemical light stick, etc. are all things that will maximize your chances of rescue once SAR is in the vicinity of your PLB ping.
With that in mind, I think the absolute best way of storing a PLB for diving is to use a canister right can with a blanking cap. The extra space above and beyond what it takes to store the PLB can be utilized to effectively store this other aids so that they are readily available. At night, buzz-sawing a chemlight is like a nuclear explosion to a set of NVG's. A dye slick gives a rescue chopper a far bigger target. Things like that when carried in a canister may be the difference between being rescued and being lost at sea
Light Monkey offers cans, or a more economical solution is to buy and old non-functional can light to scrounge the canister. You can easily blank the cap penetrations with common hardware, and some silicone.
They are also designed for depth and attachment. Personally I rig mine so that I can remove it from my belt and still maintain control of it with the use of a simple deco bottle leash.
Being equal or less expensive than dedicated solutions, they offer a much better value in terms of usability.
