my daughter uses Oxygen 24/7 too. Last year on our first cruise, I called her supply company and talked to someone in the national office. They told me they wouldn't supply or deliver tanks to the port for us to take out of the country. So, we got tanks ourself and took them on the drive to the port. I bought a rolling hamper and put them in that (8 tanks) & left them with the porters. All labeled with our cabin # & her name. We took her concentrator with us onboard. She used that at night. When she needed another tank during the day, I called for it and they met us & we switched out tanks.
This year, she has the Airsep Freestyle and we are getting the battery pack soon to extend the life. I will still get a few tanks to take for back up when we are out & about if the battery dies.