I'll try to add more detail later, but I will outline the basics with the pictures I have. First, I needed something to cover the scooter itself since the Witch's skirt wasn't large enough. I just got about 4 yds of cheap black fabric and stapled (faster than sewing) it together to make a larger skirt.

I needed something to keep the skirt out of the wheels so I bought some cheap Lawn Edging material at Lowe's (since they had the smallest spool). I then made a ring and supported it with bracket at the back, ties of string to the main post for the sides, and a tied the front to the anti-tip wheels in the front of the scooter. This allows the caster wheels to spin freely without catching the fabric.

Once I added a bracket projecting off of the bolt (centered between the caster wheels), the hoop's shape was more oblong (not as wide side-to-side). I just secured the Lawn Edging to the rear bracket with Velcro to allow easy access to the batteries and you can see I used cable ties to secure it to the front ant-tip wheels.

I just used a 1 1/2" aluminum tube I had to go into the seat post of the scooter and then I placed the Witch, which sits on a smaller post as part of her stand, into the post and ran a screw through both to secure.

This is a picture of the Sabertooth 2x32 Motor Controller installed. I just left the stock motor controller on-board to use for charging. I disconnect one and reconnect the other as needed for now. It comes with set-up software which makes it fairly easy to get set for the RC Receiver. It also has a BEC (Battery Elimination Circuit) which supplies the 5V the RC Receiver needs.

Some details included adding an RC Relay Module to trigger her voice on and off. It works well as it toggles on/off sequentially with a single relay. Instead of double-sided taping the skirt to the Lawn Edging I tried using wire-wrap Velcro (non-adhesive) to wrap around the circumference so the bottom edge of the skirt would look loose. It works well ans since it is black it isn't noticeable at night. I also gave her a cheap LED lantern from Target and just zip-tied it to her hand. It is able to swing a little as she turns and zips around.

UPDATE:  Waiting until the day of Halloween is a great time to see what some stores put on SALE, and I was able to purchase a "Hell Rider" animated skeleton on a motorcycle/chopper.  This turned out to be a great upgrade to my rig, and I was still able to use the witch but attaching her on to the back of the motorcycle (supported by the scooter's foot rest), riding "witch" if you excuse my terminology.  I attached my RC Relay to trigger the motorcycles sounds and I added a Halloween-themed door-knocker to the handle bars above the working headlight.  I took it over to a local car show on the morning of Halloween and I got a lot of positive feedback, and I think the motorcycle is less scary to the kids than the witch was since the witch looked more real and haunting (people thought it was a real person in a costume on a hoverboard).