I have Lupus among other things and usually use my own scooter. I only use Disney buses. Since I am familiar with the scooter, it is easy to get on and off buses and boats. Just remember to do it in turtle mode.
As a matter of fact,
a whole boatload of people stood and cheered after I easily parked on a boat from POFQ to DTD--it seems that someone with a rented
ECV had just given up and exited the boat at POR after trying to go full speed and running into other passengers!
It probably helps that I parallel park my ECV in my apartment to store it and do this several times a day!