I am on the same type of treatment as the OP. And I have to agree with LockShockBarrel. Your immunosuppression is not so deep that you are at great risk from being in the average waiting area. Frequent handwashing and use of hand sanitizer is probably all you need. You're probably going to be at higher risk from being in an aircraft flying to WDW than you are once you are there, so long as you take the normal precautions.
I'm not sure any kind of GAC is going to protect you from the Florida Sun. There are very few waiting lines that are totally unprotected. The vast majority of your sun exposure is going to come from just getting from place to place. Get a really good sunscreen and use it. Liberally and frequently. Wear a hat that shades your face and neck. Wear a shirt with sleeves. (short sleeves at least). I usually wear a tank top with a light cotton shirt (unbuttoned) over it. Seek shaded areas to rest in (plenty of those are around, you just need to look.) During the brightest part of the day (10-2) try to stay indoors: eating lunch,
longer indoor rides and shows.
The
scooter will really help with your mobility issues, but your sun sensitivity and immunosuppresion are issues that you should be able to take care of yourself with just a little extra care. A GAC wouldn't be of much use.JMHO & YMMV