I used to have a 43DS and now have a bigger boat. I've got 2 scuba tanks and a Bauer Junior II compressor aboard. I don't know where I would have put that on my 43DS, I don't know if it would fit in the cockpit storage area. In addition, it takes a big surge in power when starting (it isn't bad on energy while running) and if you have a 5-6KW generator then you would need to get a "soft start" option.
Sometimes you just have to look at a problem through new eyes... My Son was having problems making the flow of his lounge work after taking delivery of a new sofa. Everyone else could see if he moved a small bureau and standing lamp across the room all worked well, but he didn't want to do that - He was used to seeing it the way it was. We finally convinced him to move everything around and live with it for two weeks, now he cannot see why he didn't do that in the first place.
I have no idea how big your tanks are but I have seen a couple of compressors and they would fit neatly into the Life raft garage. Life rafts can be mounted on the stern rails. Tanks would probably fit in the port side deck locker close to said garage. Or maybe make a rack for them under the floor just above the keel where the weight would be centred in the boat.
If like many you have put a genset in the garage then consider moving that. I once viewed a 43DS where they had put the genset into the deadspace just forward of the chart table - The space aft of the nav table is where the water tank switching is, the other side of the table support is usually empty. He had put the genset there so he could run it without having the noise in the aft cabin.
not sure I'll be able to convince the wife to let me buy a bigger boat so I can fit the scuba compressor...
tanks are 2 x 10L and 1 x 8L yes, that could actually work. that locker is only used to store fuel for the dinghy, and I have the genset aft of the chart table already I have to clean the lockers as I have the diving gear on that one and 2 inflatable SUPs in the starboard side one, and not sure I want to keep tanks inside the boat
Before narrowing down the compressor - do you have a generator? If so, how big is it? If you don't have a genset, then you would need a compressor that is gasoline driven and that narrows down your options. On my 43DS I had a generator in the liferaft compartment; if your generator is elsewhere and 5KW or more then the liferaft compartment is large enough.
Despite my brother being a professional diver for most of his life I confess I know nothing about scuba. I have however, looked at that big empty space under the floorboards amid ships and pondered that it is a useful area going to waste. No doubt a good chippy could make that into removable and useful storage.
How many times would you need to empty it to check on the keel bolts? Once, twice a year maybe??
What about storing the bottles on the stern rail? I have seen that on a few boats.
I was suggesting the space to be used for the actual tanks - not the compressor. Personally, I wouldn't put much in that space that has high voltage electricity connected to it, but it is a big area of wasted space.
As a matter of fact, as part of the upgrade of the saloon table, the plan is to be able to access that space from above.
By having a single pedestal I'll be able to turn the space around as storage, and in that empty space I'm going to divide the bilge and create an access from above, so I can have a long storage space for foods, clothing, etc., I'll add a double floor, for easy storage and access
I'm also thinking for the scuba tanks to engineer a support either between the Travellers and the dodger, or around that top deck.
My plan is to mount the life raft on the side of the arch, but not yet, watermaker and Lifepo4 upgrade are at the top of the list before the liferaft as we donot do offshore yet
We don't have a compressor, but I usually carry a tank, in case I need it. We store the tank outboard of the arch between the arch and the corner guardrail. Two tanks will fit on each side, but I only have one. The bottom of the tank sits on the rail while the neck is exactly the right height to tie to the arch.
The two bicycles also fit nicely into the slot outboard of the full enclosure, one on each side. They are aluminum and not many parts rust. I would not leave them out here on an ocean crossing (dinghy goes up on deck, too), but for coastal cruising, this is much better than taking them apart and stowing below.