I went on the evergo web site and looked at it. It seems it does not have a cart, so you will have to carry it with you wherever you go. That's 10 extra pounds- it sounds heavy. DD has her own wheelchair. We use the cylinders- I just find it easier than the POC. We tried the POC, just hanging it from the back of her wc, but it was always sending out alarms, and if I was away from the wc , DD couldn't reach the machine to stop the alarm. Also, I was continually going to first aid to store extra batteries, charge dead batteries - it was always on my mind and didn't contribute toward a restful vcation.
Now, we use the POC on the plane and getting from the airport to the resort, but get the oxygen service provider down there to deliver cylinders when they deliver the concentrator to the hotel. I have 2 holders for the cylinders on the back of DD's wc, or I can store a cylinder at first aid. DD is on 6 lpm so a E cylinder lasts about 4-7 hours. She breathes very fast so the conserver pumps the O2 out fast. You are at 4 psi in flight, but you didn't say what your needs are on the ground. I'm assuming they are at 2 or 3 psi. A cylinder will last you a good long time. You mentioned a scooter. I know you will lose some independence if you transfer to a wc, but you may want to consider it if you have someone to push you. Many rides are wc accessable but not scooter accessable. If you are using a scooter, really all I can suggest is on some rides such as POC transfering to a WC, and hanging the POC off the handles. When you go on the ride, the wc will be waiting for you where you get off. If you take your POC with you on the ride, there is the posibility it could get damaged. I suspect you could go a few minutes without the O2,since you will be sitting in the boat, in which case the POC will be ok, leaving it with the wc. make sure you have it shut off so no alarms are going off.
On rides such as Peter Pan, just carry it on board with you. a gentle ride such as that should not bump or harm the POC.
Just another thought. Do you have a backup plan in case the POC gets damaged? It's a fearful thing to be dependent on O2. It sounds like you do not have a company to look after you down there. We use Lincare. Our O2 provider here at home forwards the presciption to them and they look after us very well. Any way I can help, just let me know. And have a safe trip. Make lots of wonderful memories.