Thanks, folks! In answer to the question: yes, I use a single Nikon SB800 in its own Subal strobe housing. The iTTL works pretty well and the strobe has plenty of power, although I have to be very careful with strobe placement.
G'day, Bruce! I'm still recuperating from the surgery, slowly but surely. I think I'll be fit for diving in a few more months.
G'day to you too JimmyC, . . . .
I always study your pictures 'very' carefully, ( just to see that they haven't been stolen. . .

Nah, Just kidding. . .

) your lighting always seems to be spot on.
If you look at the current pic you will definately see shadowing but it is understated and natural, certainly not sharp or over bearing. An old craftsman chooses his tools wisely and then learns how to use them. The SB800 is a very capable tool in the right hands, and it seems as if you have a pair of those hands JimmyC.
Hooroo JimmyC, your a bonza bloke,
Bruce...