Hooking a rotisserie up to the Weber Jumbo Joe is fun as heck! I will be the first to admit that my approach makes no sense from a financial point of view but this is my hobby so I tend to throw economics out the window at times.
My rotisserie is the ring model that Weber sells for the 22.5 inch kettle. The rotisserie ring costs about $130 and comes with free shipping from Amazon.
I support the ring with eight bricks (four on either side of the grill) and center it over the Jumbo Joe. The lid on the Jumbo Joe will not close with this setup. Instead I place the lid in the vertical position in the lid holder and use it as a wind break while I cook with an open air rotisserie.
The open air rotisserie works much better with a charcoal grill than a gas grill. With a charcoal grill the extra air makes it burn hotter so you really go through the fuel and get some nice searing heat on your meat.
Here is a short video clip I put together using the rotisserie ring to roast a chicken. I was adding a little more charcoal to the banked fire about every 15 minutes.
A more economical approach is to use the Grizzly Spit
Be sure to check out some other Weber Jumbo Joe Upgrades!