Well, it is raining so I finally have time to report.
I wanted to cook low and slow as much as possible so the setup was indirect with a single Weber Brand indirect charcoal basket. I placed the lid on for about 25 minutes to sear the roast. After that I left the lid off. The heat source was only on one side this way. After three hours and 20 minutes, the roast was up to 128F internal when I pulled it off. Removed the twine and tented with aluminum foil until we were ready to sit down and eat. The roast produced a good amount of drippings to add to my au jus recipe. Everyone liked it.
Basically, the only advantage of cooking it this way is to not use the oven in the house on a very hot day. The charcoal did impart some flavor, but not much. The natural self basting of the rotisserie method produced a good tasty crust.
