Stink sleeps with me in the canoe, its too cold out at night. In the discovery 119, what has worked best is two sleeping bags, he gets in the first one, then I get in the second and put him under my knees, so my legs are on him. Its warmer that way. He does add some condensation, so there will be more "snow" in the morning, but its fine. I'm 5'9 and 180 at the start, he usually starts heavy at around 75 pounds. But small space with a dog, should be no problem. The two of you will work it out.
Fascinating to me how long people and dogs have been doing these things together. We are made for it.