I too am on a dive trip now, and setup my lenses with the inon LD mount adapters, and always tethered with a fishing line. Even then it doesn't let water in, so I just have to mount it underwater, which is less of an issue with the bayonet mount.
Everything has been working fine this far, and there are 2 more meikon/nb branded users on this trip with no issues this far(keeping fingers crossed). Just find it strange that the similiar range G16 housings have double o-ring and no leak sensor.
With regards to manual settings, the aperture should be in the front ring in M mode. To change shutter speed, you have to go into S mode and use the front ring to adjust, before changing back to M mode. A hassle it is for sure, but I generally keep shutter speed at 1/125 to freeze motion.
I had a stainless steel fishing line leader attached to a zip tie that was wrapped around the lens as tether. I was always afraid it would drop while the cable was somehow wrapped around the fiber optic cable and slice it through if I drop the lens. Then I made some floats that wraps all around the lens, thus making underwater re-attachment pretty much impossible given the float blocks all view of the mating area of the thread. For the new RX100 setup, I didn't use the float because the reattachment of the lens requirement underwater, but left the tether off.
I meant I wanted to change the shutter speed since in re-taking a picture, I did not want to change the f-stop, which will cause the strobe to have to throw more light, possibily causing underexposure or the foreground subject becoming more bluish if the strobes maxed out in its light output capability. If I increase the shutter speed, only the background gets darker.
Jumping to S mode to change shutter speed would likely not work since I shoot mostly in MR mode, and MR 1 is pre-configured for shooting wide w/strobe under M. If I jump to S and then to M, it would not have any of my settings in MR 1 (iso, metering mode, etc). MR 2 is shooting w/o strobe w/manual WB, higher ISO, Shutter priority, etc, and MR 3 macro w/strobe.
So I either have to commit into memory how to change the front ring's mode from STD to Aperture so I don't forget about it when not touching that feature for many months, or get rid of MR 3's macro mode (a useless mode anyway, probably will just carry another P&S and use it to shoot macro with its built in flash..and put it on a pole so I can stick it into holes and get video that the big rig cannot get into) and have it similar to MR 1, but it will be in S instead of M, so as to let the camera's metering adjust settings so it exposes surface/sunball on par with forground exposure.