In the recent thread about Amel yachts there was a youtube link to the yacht Delors and their circumnavigation. The video provides a detailed tour of the yacht fittings including dive equipment and the compressor, their bottles are mounted on the aft deck and this is a 50 footer. I know zero about diving but the youtube video confirms the point about needing an onboard compressor away from the usual yachtie fleshpot locations.I am not sure I would want to store the cylinders on deck for any time for all sorts of reasons.
The OP should watch those youtube video if only to provide more inspiration for the circumnavigation.