Dwain-
Yes, as Paul mentions above, you can order the rings as "replacement" parts. I had one from my rotisserie, and just ordered one extra.
Albert-
I used a 20"x2" cake pan, and mostly used sand. I didn't want to mess with that amount of water, and as you can see, there's no access door to replenish, so sand was a bit easier.
All in all, this was an easy project which allowed me to continue to use my kettle for its intended (grilling) purpose, and to also use it as a large, vertical, water smoker. I did not have a WSM at the time, and converted my kettle for the cost of the ring ($30), and some hardware (about $15.)
If anyone would like a blow by blow of the demise of my kettle, I'm sure that Henry Joe or Rick Jones would be happy to jump in (HJ has some video.)
If you are interested in specifics about how I did this, feel free to ask here or send me a private message. FWIW, I got the idea from someone who used to post here (Webb Collings), and his version was much prettier than mine (read, he has more tools than me. /infopop/emoticons/icon_wink.gif )
Cheers,
Rich G.