I love my gatorskins and think they are fine on firm and somewhat smooth unpaved surfaces. I wouldn't use them if I expected much loose and deep sand, loose gravel of any depth, or mud. I would use them on most crushed limestone surfaces. I don't mind pushing or carrying the bike over short distances of bad surfaces but id much of your trip will be mud I'd probably use a different tire.
Personally I prefer to pick routes that are either:
- Devoid of a lot of poor surfaces where I ride road tires.
- Off of the pavement as much as possible where my mountain bike makes sense.
If I do go somewhere that will require more serious off road tires, I like to go with cross country MTB race tires. Something like the Kendal Slant Six or the Stans No Tubes Raven with lots of small low knobs works well. In that case I take the mountain bike and stay off pavement as much as I can.
Basically I either avoid the dirt as much as possible and take a road oriented bike or embrace the dirt and take the MTB.