If you don't plan on wetting, something like a GoodNite would be alright. Wear a long t-shirt or keep your shirt tucked in to keep everything covered.
If you do have any intention of wetting, make sure you're wearing something you can trust for how much you plan to let out. You don't want to have to explain a wet patch on your pants to family members. But also remember, the thicker the diaper, the more noticeable it's going to be. Plastic-backed ones might emit a crinkle others can hear.
Also have a plan for disposal. If you're going to be sharing a hotel room with family, for instance, you probably won't want to leave used diapers in the little trash cans in the room, even if they are bagged. If you carry a backpack, you can take them with you until you can toss them discretely.
Finally, a few more words of caution. Take care if you'll be travelling with other males and may be entering public restrooms at the same time. You'll probably want to use a stall over a urinal without a divider as a precaution. (I'm a girl, so I don't really know that much in that department though
) Diaper crinkle might be audible while removing it in a restroom stall, so keep that in mind too - and those silly gaps often present between stall doors. Family probably won't be staring at you through them, but again, something to keep in mind. Maybe take a stall farther away so they won't have to walk past you on the way out, if you're concerned.
I hope this didn't scare you out of your plans!