I have the Masterbuilt Pro smoker & like it very much so far. First of all, let me say that I don't think you'll ever get the smoker down around 100 deg. I love smoked cheese & do not use any heat to speak of, especially the propane burner or charcoal, when doing this. Cheese needs to be below 90 deg or less. I use a Smoke Daddy generator attached to the smoker & that's all. Of course it produces a little heat but not enough to melt the cheese.
As for the salmon, I smoke salmon quite a bit using the propane burner for heat & the Smoke Daddy for the smoke. I have the burner down as low as it will go & the vents open all the way & I can barely hold it around 200 deg. Sometimes, if the temp starts to rise, I'll also crack open the bottom door a bit & this helps keep the temp down. A couple of weeks ago, I smoked two slabs of salmon for 3 hours with a temp fluctuation between 185 & 210. It worked out fine & the salmon was delish. Sometimes I will throw the fish in the smoker & smoke it for about two hours like I do the cheese, then transfer it to the propane grill to cook it.
If using the propane burner, I don't know how one would get the temp down to say, 150 or so. I don't want to use charcoal in this smoker if I don't have to. For me it's just too time consuming to control the heat. That's the reason I went with a gas smoker. After all, the propane, electric or gas are used to supply heat. The flavor comes from the smoke, however you elect to get it in there. Besides the Smoke Daddy(www.smokedaddy.com), another smoke producer you might want to look at is the Amazing Smoker(www.amazensmoker.com). Check them out. Hope this helps.