Coral Sniper, you can't go wrong with 140 RA. I'm getting myself a new one (it's on its way), which I intend to use for bluewater hunting (except for big tuna) and, downgrading shaft and bands, for skittish fish up to 10 to 20 lb. in the South Pacific, like you.
You need not load 2 x 19 mm, it's too much power for the rig weight, even with 7.5 mm shaft, and maybe the trigger mech. 2 x 18 or 2 x Dessault's 16 mm, but only using 7.5 mm shaft will be fine. With a 7 mm shaft, the standard 2 x 16 RA bands are plenty, perhaps even better would be one 20 mm band.
My rig will have 2 x 16 mm with the 7.5 mm (and breakaway) for big game (over 40 lb.). When in places like you described, I'll take one band out and use the 6.6 mm shaft. Those shafts are as though as precise. In a recent trip, I shot 7 amberjacks over 25 lb. in three days with a 6.6 mm x 150 cm RA powered by one 16 mm band. Good as knew. I know for a fact that RA is an upfront bloke, but, as St. Thomas, I wanted to see it by myself to believe. I'm sold. Here below are the first 3 victims.