You could dress up as a nun and go as Virgin Mobile.
Or not wear any pants and tell people “I’m the Oscar Meyer Weiner Mobile.”.
Doable but may be misinterpreted at children’s parties.
Ah. True.
I want a power chair so I can make it into a sedan chair … with long fringes to hide the base and wheels. It would make the job of the ‘slaves’ carrying the chair much easier. Or I suppose I could make a couple of dummy ‘carriers’ to mount on the front and back handles. 
[My SCA persona is roman, and would use a reclining litter rather than a sedan chair proper, though my secondary one is an Elizabethan woman, and she would use a sedan chair. My shu-nu-shi is a horse riding nomad, so I wouldn’t use a chair of any sort there.]
For Fantasy/SF purposes, I could make a big almost transparent bubble and go as a haut woman in her force bubble enclosed float chair …
I’m also thinking of a Dr. Who costume, with a big foam-core TARDIS over my chair to ride around in.
Instead of Davros, Daleks or Tardis, why not go for that rolling companion, K-9?
No thanks.
I’m sorry your condition has worsened, BMalion. Is your MS relapsing-remitting or chronic-progressive? My SiL has C-P MS and has been in a wheelchair for about 12 years now, but has a pretty active life. She lives with her sister’s family which includes four kids, and is also over at our house (2 more kids) pretty often. I’m gonna suggest some of these costumes to her, maybe she’ll let us take her out next Halloween!
Chronic-progressive.
I’m sorry, that’s a bitch. I hope it progresses slowly for you and that your new chair makes it a bit easier to get around.
Thank you. Everyone has been so kind, I appreciate you putting up with my nonsense.