I've been wanting to try an extended cook in the Webers, using the "snake" method. I set 'em up the same to cook a butt in 2 pieces. It worked! One of the grills held temp for almost 8 hours before the temp began to drop (7 hr 56 min to be precise). The other followed shortly thereafter.
Whilst the butts were smokin', I put a couple of racks of babybacks in the offset and let them go for 3 hours before wrapping & cookin' another hour. The video shows one of the racks on the Weber as we were finishing up with the sauce.
Everything turned out.