Hi freemore,
I'm one of the "pilots" for the MK area boats. You'll be fine with an
ecv. Water level is not a problem with the boats that can accommodate the ecvs at MK resorts. The cruisers (the large white boats with the green flags) dock at floating docks at MK, WL, and FW. The docks rise and fall with the water level, so they stay even with the boat doors.
The launches(the ones that look like small steamboats) dock at the hard docks that stay at the same level. There have been times where there might be a 12' step up to the dock, but those boats do not accommodate ecvs.
See ya real soon!
Bill