The Ramada Inn in Grayling is an old hotel, huge. With a parking lot to match. Stayed there a few times. "Clean and Dated" with great prices. The trail runs along the back of the parking lot. There are places to eat and have a beer in walking distance or a short ride. The Days Inn to the north of The Ramada is another option. The trail goes through their parking lot as well.
The trails system connects with Frederic to the North. Look up Sleadheads of Frederic. They are fantastic. Some of the most honest trail reports in the area on their web site. They also have cabins to rent and can guide you as to other options for where to stay. For a nominal fee, you can park in their back lot for the day. It should be able to handle your rig. Or the trail head parking lot about a mile to the East, as long as your turning radius is not too tight. I have heard Sleadheads also has a gated storage lot just south of Frederic to stash your trailer if you need to.
Some great rides to the North and North West out of Grayling. And also South toward Houghton Lake, and then East toward St Helen.
There is a trail head parking lot just to the North East of Grayling that connects with a great trail system to the East. It might be tight for a big rig. However, the trails from there wind around to connect with those in Grayling.
The whole area is very snowmobile friendly. Sledding to get gas or a restaurant was seldom a problem. Just used common sense and followed the tracks. There are lots of tracks.
Some other considerations. The trails out of St Helen connect with those in Grayling. The trail system around St Helens is among my favorites. There are two "Trail Head Parking Lots" in St Helen. One just off the Interstate that would not fit your trailer. And a second just to the south of their Airport. On the East side of St Helen. That one can easily handle any size truck and trailer. Many over size rigs would not be an issue. There are trails that connect the parking lots. Many main trails and lots of side trails to explore out of St Helen.
Depending on the snow, we would sometimes start at the trail head just north of Clare in Harrison. That parking lot is big, with room for a larger rig. But it fills up later in the day, so get there early to have a clear shot of getting out to avoid getting boxed in.
Last winter had a lot of "iffy" snow days. So we would generally check to see where the fresh snow was, and head there. Between St Helen, Frederic, Grayling, or Harrison, we had a fantastic season. Especially during the week when others would stay away because of the reported lack of snow. We would frequently have the trails to our selves with 3 inches or so of fresh snow. Enough when it is just you. :- )
So that might give you some other area options.
Let me know if you have questions, but suggest Sleadheads of Frederic as a place to start.
_Jack