There are a couple spots just to the north/east of the State Park that you could park the truck/trailer and unload (depending on the size of your rig). That would put you closer to camp and more in the middle of the trails.
County roads (not forest roads) are open in Montmorency & Presque Isle counties, so you can use them to connect the trails - just can't get in/out of the State Park on an ATV.
The trail is tighter for ATVs in many sections, even though it's a 50" trail, but the route is pretty nice and wide. Depends on what type of riding you prefer.
Gas and food are right on the trail, on M-33, towards the northern portion of the loop.
Most of the mud should be pretty dry right now, but I've not been on there in the last couple months.
Have a good ride!