I've got a touchy kid who also happens to have SPD (sensory processing disorder). So I know exactly what you mean about LO being overwhelmed my new/unfamiliar enviornments! That is my kid to a T!
What I've done when we travel is bring several familiar objects from his bedroom. Our wind down consists of saying night-night to several objects, so I try to bring as many of these objects as possible into the new room. Then, during wind down, we say night-night to familiar objects as well as to the new objects in there. I also say with him until he falls asleep, even though we don't do this at home. Whenever possible we have him sleep with us in a portable crib so that if he wakes in the night mama and dada are right there, and he feels safe.
Another thing you might try, since you're going to your sister's house, is have her take pictures of the room where he's going to sleep. You and he can look at the pictures every day until you travel and talk about where he'll sleep, where mama/dada will sleep, the fun/cool things about the room, etc. Since he's 2, you might buy some fun thing for travel sleeping -- maybe a neat sleeping bag with characters he likes? Maybe a fun glow in the dark animal or one of those fun turtles with constellations on their back. Something really exciting and fun that will make it seem more like an adventure and less scary. You might also get some books at the library about travel/sleeping in unfamiliar places to help talk about it more.
Because my son has SPD we have to do this type of thing for just about everything you can imagine. The key with my son is to walk him thru the steps of the new event. So, in your instance, I would show him pictures of the room, talk about where he'd sleep, talk about the fun things we will be doing at the new place, and explain where mommy will be in case he needs her. Don't worry about AP on your trip -- the main thing is to make sure child feels comfortable and secure. So by all means stay with him until he falls asleep and do whatever comforting things he usually likes.
You may also be surprised at how different he is now! Even with my son's sensory issues he amazes me at how much he changes just from month to month, let alone year to year. So as much as possible try to be excited and upbeat and he will probably catch on. I hope it goes well for you! The cruise sounds like fun!
