I have a couple of questions for you. Some say that they are "Smoking" fish, when what they are really doing is just running a pan of smoke against it and then completing the actual cooking by another method, such as frying, broiling, BBQ etc. Then, of course, there is what is normally termed "Smoking fish", where you smoke and cook at the same time and continue the process until the fish is actually ready to eat. I presume this is what you are doing. Let me know for sure. Your answer could alter our suggestions.
I also see that many use the same method for virtually every kind of fish. This gives mediocre results much of the time. Just as beef and pork "CAN" be cooked the same way, almost all fish "CAN, as well. But, just as in meats, you are usually happier if you use a method that is proven for each specific fish. That goes for brine composition, brine times, as well as cooking or smoking method.
Also, some Smoke fish at fairly high temps. They get a thick slab of Salmon done in just a couple hours brcause they have their temps way up. Well, it may end up kinda smokey, but I think they just cooked it, not smoked it.
Salmon wrote the book on the old saying "Low & Slow". Salmon should be smoked at a fairly low temp. If 'cold' smoking you should be at 90F to 110F. If 'hot' smoking, most people I know like to stay between 140F to 150F. Try PMing with 'Salmonclubber'. He is a fishing machine and smokes every type of fish and wild game you can imagine. He brines a little differently than I do, but he will confirm and share info on temps and times.
A Salmon of normal thickness will take from 3 to 7 hours to smoke, low and slow, at 140F to 150F. Much of the difference in times is due to the outside temp, thickness of the fish, amount of moisture that was leached out during the brining process etc. There is no set rule. Just like meat, it is done when it is done.
The problem is that most smokers are not meant to run at this low temp. Therefore they do not make good Salmon Smoker.
Everyone here has asked some very good questions and given you very good advice. I agree, I think the vents are OK. I also agree that some woods are too strong for Salmon. They may not be bitter when on a nice cut of beef or slab of pork, but thay can be on fish. I would suggest Alder. It is the most commonly used throughout the nation, for Salmon. I would also mess around with your smoker temps. Try to get down to that preferred range. My new GOSM verticle couldn't do it, so I had to buy an inline needle valve that gave me better adjustments. I can now successfully smoke Salmon, yet get high temps when I need them. There is info here on the valve and if you can't find it, PM me and I will help you.
Many of us have multiple smokers. Some are just better for one thing than some of the others. As a last resort you may consider buying a cheap electric Leur Jensen Smoker. They were developed out here in the Pacific NW, specificly for Salmon. $65-$75 new and at garage sales for next to nothing sometimes.
Sorry for the long rambling post, but wanted to share a little of what I have learned smoking fish. Hope it helps