Thseng, that covers most everything I was going to cover in terms of types of shelter, but I might have put the pit at #1 if you are soloing- small volume means you have to use less heat.

Your biggest challange is staying dry. Most snow mobile gear is very insulative, but if you have to dig, take it off. It is better to be a little cool and not sweating than warm and sweating, becuase once you stop moving, you might as well be sitting on a sheet of metal. You'll be loosing something like four to five times as much heat if your soaked than if you are dry, so while you might yelp when you put that icy cold jacket back on, at least it will warm in a few minutes.

If there is a group, you want a group shelter: cuddle like a man, or freeze to death. Group heat is good heat, particularly if you have a shared moisture barrier and insulation layers below you and insulation above you. Humans evolved in a temperate grassland, we waste most of our heat, so using your buddies as external heat sources is a good thing. You might not get much sleep, but you have a better chance than if each of you were in individual shelters.

Either alone or in a group, looking over the list of gear you've got, you should be good. The only thing I didn't see was a sleeping bag and a moisture barrier bag for it, but that's an item most people don't ride with becuase of the bulk and I guess I can understand it. One thing to keep in mind is that you do have your machines, and while canniblizing them isn't usually the best option, using them to form part of your shelter (wind break/heat reflector/wall, or maybe even an anchor point) isn't a bad idea. Remember, it's a couple hundred pound weight, it isn't going to blow away.

Are you carrying an family band radio? A lot of groups around here use them, so if you hear a machine and start cruising the channels, you might be able to signal someone.

There is no one shelter I'd recommend, because I know if you've got someone injured or who has taken a soaking, if you've got a lot of dead trees around (they are called widow makers for a reason), is it actively snowing, do you expect your lostness to be noticed soon? If I don't have to worry about things landing on me, I might go with the tree shelter. If I do, or can expect a search party, I might do a trench in an open area if the winds aren't horrible. The only reason I'd do the big fire, in any season, is to signal. But in any case, I would stay close to the trail. Never seen a trail that didn't have night traffic unless it was inhumanly cold out, and most trails are generally within a mile or so of a roadway, so you might be able to hike to it in morning.