I'm really big into snowmobiling. I've been riding in CO and WY for the last 10 years, including working several winters as a snowmobile guide in Lake City, CO. A big reason I continue living in colder climates is my near obsession with snowmobiling. If someone said I had to give up my Toyota or my sled, it would be the personal equivalent of Sophie's Choice.
Due to weather, gas availability, and trail conditions, lengthy trips are tough to come by. One of the best trails for a "long trip", is the
Continental Divide Snowmobile Trail, located in WY and MT. This trail is 365 miles and will take you from Lander, WY to Yellowstone National Park and into the town of West Yellowstone, MT. One could opt to continue into Idaho as well. This trail is consistently rated as one of the top trails in the west.
The big consideration is gas. Sleds normally have a 9 to 11 gallon tank. To make this trip you would need to carry gas cans, even though there are gas stops along the way. I have mixed feelings about snowmobiling in Yellowstone, but those who have done it generally rave about their experience. To snowmobile in Yellowstone you must make arraingements with one of the many tour guides in the area. They no longer allow individuals to snowmobile in Yellowstone. Only 4 stroke "clean machines" with a tour guide are currently allowed in the park.
Due to insurance liability, most operators who rent sleds also require a guide to go with you. There are still a few who may turn you loose after a brief training course. Something I enjoyed doing was taking the sleds up and renting a Yurt or Haute for the evening.
There is a great system in the San Juans of Colorado, the Hinsdale Haute Route Being alone on a snow covered mountain, in a Yurt with your favorite libation, a fire in the stove and your main squeeze, under the clearest sky imaginable....Nirvana!