Reputable forum? The best you can hope for are reputable contributors on a forum. Either way, you'll need the ability to separate the wheat from the chaff. There are several subs on reddit that cover smoking, BBQ, Traeger, and I'm sure a few others. Outside of that, I'm sure an open search will find some others to peruse.
As an avid brewer and fan of all things cooked outdoors, I seldom frequent forums dedicated to BBQ and smoking. I do sometimes look at what's new on BBQ pit boys, amazing ribs as well as some other sites. There are a few members that contribute to a thread I started on Brewers Friend early in 2018, titled, "Smoking, grilling and curing foods, etc." No real pros here, but a good group that like food.