I, too, am going on a cruise next month. I'm going Carnival which, in the past, was always okay with smoking on their stateroom balconies. That, however, has changed. All "smoking" (cigars, pipes, tobacco, e-cigs, APVs and whatnot) is relegated to certain areas of the ship. The balconies are now off-limits. If they catch you smoking on your balcony (be aware there are camera's monitoring all sides of the ship for "safety reasons"; drunks overboard, suicides, etc.) they will assess a $250.00 "cleanup and refreshing" fee on your account. If you're going Carnival, their web site gives all the rules and regs.
Now all that being said; two years ago on a Carnival cruise I fell on the water slide and broke three ribs. On day 2 of a 7 day cruise. S'wonderful. I spent the entire cruise laying in bed in pain. Yes, I vaped my .... off. I was using GreenSmoke cig-alikes and my carto of choice was Mocha Mist. GreenSmokes never had any lingering smells. Nothing was said, no fees assessed. I asked my wife each time she came in the room if she smelled anything, she always said no.
If you blow huge clouds that fog the hallway when you open the door, or prefer a liquid that has an overpowering scent that lingers for days like an old southern church lady's perfume; yes you WILL get caught when the steward comes in several times a day, or a "rules zealot" neighbor sees you pluming and turns you in. Also, I'd leave all my gear in a drawer or a bag, not on a desktop or table top. No need for anyone to see your vape gear.
Treating your room steward as a new friend and not as an indentured servant will go miles in what he "sees". Being I was room/bed bound, I got to talk to him several times a day as he worked. I learned of his kids, his wife, how he likes his job, etc.. In fact, one time when I shifted in bed when a rib "popped", my e-cig fell of the floor from under my covers. He motioned for me not to move and he picked it up, handing it to me with a smile.
I still use GreenSmokes at work and in the car, at home I use an Aspire with a Nautilus Mini. I will be using the GS in the room and stealth vape on our balcony. The Mini will be used at port, in the casino and other dedicated areas onboard. The Halo liquids I use (Tribeca and Café Mocha) have scents that linger for quite a while.