I know I'm a little late to the party on this one, but what part of the animal is this roast from? Different muscles have different fibrous tissue compositions and will cook differently - this is important to remember any time you make a roast on the smoker.
I have to say I agree with the folks saying to inject, but I'd lean more toward vegetable broth than beef for deer; I think that there's a kind of sweet element to the veggie broth that really knocks down the gaminess of the deer. For the seasonings, I think if you were to treat it the same as you would a beef roast or brisket, you'd be in the right ball park. Make sure that you coat the thing with canola oil before you apply the seasoning and let it rest overnight. During the smoking process, you definitely want to use a baste or mop of some sort so it's probably best to smoke something like this in a roaster pan, then just baste every 30 minutes or so - this will keep it from drying out and hopefully tenderize the meat. As for temps, you need to make sure it passes the USDA mark for 160* for safety's sake, then I'd pretty much monitor it to see when it's fork tender. I've found a wide disparity with wild game for when it becomes fork tender; for deer I've had it anywhere between 170-190 using a similar method and with other animals (elk or moose) it varies significantly as well depending on the animal. Since you're monitoring it as a fork tender piece, you'll know if the texture is getting tighter or looser as the cook progresses so as long as you're attentive, it won't turn into shoe leather. Also, always make sure you rest deer at least 45 minutes after you cook it, there's a process that happens as the meat rests that tenderizes it. The best way to rest it is to wrap it in tin foil, then wrap that in a towel and put that into a beer cooler.