Yortchko, welcome to SMF! Glad you're here and looking for answers. Since it's Tuesday though, I'm guessing you're long past the need for an answer.
Personally, about the only time I smoke tri tips anymore is when I have several to smoke, or am smoking more than one type of meat. They only need about 2 hours of low temp smoke, then a 2-4 minute per side reverse sear over high heat on the grill. Otherwise they are just kind of grey looking meat.
Normally I do something I call a smoky grill if I'm just cooking one tri tip roast. I use a Weber Kettle, put a quarter chimney of hot charcoal in the baskets, put on a couple small wood chunks, sear for 2-4 minutes per side with the lid on, then move them over to the indirect heat side of the grill with the lid on until they reach an internal temp of 130-135F, which usually takes another 40-50 minutes.
Let us know what you decided.
Enjoy the forum!
Ray