I have a char griller as well. Not the duel griller but the same barrel style with the attached smoke box. My barrel is bigger but it's pretty close to the same.
Without knowing what your smoking I can give you this basic advice for this product.
Babysit! Don't walk away for more than 15 minutes or your could see serious spikes/drops on temp.
There is no way of timing anything on most, if not all smokers so don't play that game. Don't read that someone smoked a brisket in 8 hours on your same smoker and just assume. Every piece of meat is different, and your particular smoker has a lot of temp variations. Use a meat probe and get your meat into the safety zone before pulling it off the smoker. Just because it looks done, doesn't mean it is.
Don't open up the barrel every 10 minutes! Smokers are a lot like crock pots, and when you open them up your releasing all your built up heat. Buy a decent meat probe and trust in that. If your like me at all, trusting in the meat probe is hard to do. Trust me though it works!
Easiest meats I leaned to smoke on the offset char griller were 3-2-1 ribs, and pork butt. Very hard to mess them up.
I also like to add some moisture to the barrel so I'll drink a PBR and cut the top off the can, and fill it with water. Some people use pans, or trays, but in my experience a 3/4 cut beer can has always worked. Plus around my house they are always available.
Good luck to you guys, and happy smoking!