O.K., here it is about the cooking time with this smoker,
You’ll have to decide whether you’re going to use a water pan or not. If you use a water pan, your cooking time will be longer. The advantage of using water is to prevent temperature spikes. That means you’ll have to do a lot of vent control and temp monitoring if you're not using a water pan. Temp spikes are not a big issue when it comes to cooking chicken. And the moisture issue is also resolved (due to having liquid inside the chicken). However, when you’re cooking stuff that requires consistent low temp and a good amount of moisture (such as brisket, pork butt), you will have to use it. Again, I advise you to give it extra time, since this is your first time using this smoker.
I would never cook a Tri-Tip roast in the smoker set on low temp. Tri-Tip requires higher temp (350-375) and a combination of direct and indirect cooking method. Check out this link for cooking tips:
If you cook the Tri-Tip with the chicken for that amount of time, you will end up with a dry and tough piece of meat. It’s better to use your friends Weber for the Tri-Tips and your smoker for the chickens.
I hope this helps with your planning.