I did walk out of the bathroom looking like I had been hanging out with Pablo Escobar (the baby powder) but it can be done in a confined space safely and cleanly.

You use babypowder? I thought that was out because of the cancer risk... Even if that's not true, I really don't recommend it for travel for obvious reasons. One less item to drag (and we have enough stuff with babies!!!)

But anyway, no, it's not acceptable to do any kind of diaper change in the seat. It should be done in the lav, where there's a sink to wash and trash right there... Of course there are parents will will still but just be aware that this is not cool. Sometimes you are desperate but please don't routinely plan on doing the changes in the seat! Get up and use the lav when it's at all possible (and don't let long lines dissuade you, they usually let those with little one in first).