There are options right from Blackwater SP.
You can leave your vehicle at the parking lot at the lodge and nobody will notice or bother it.
For 50-100 miles target range, there are some good routes available.
This one would be a full 2 days:
Park car at BWSP lodge
Use the first 50-60 miles of this link
http://www.bikepacking.net/forum/routes/usa-wv-a-mountain-loop/ (Google Map Link:
https://www.google.com/maps/d/edit?hl=en&mid=17Xqo8Q3uYpgaOSzIYkEetyHWBBQ&ll=38.60446709414571%2C-79.741331328125&z=9 ) and camp along the West Fork Rail Trail. Assuming you go counter clockwise, up until you hit US33 E of Elkins it is a nice ride (downhill in the Blackwater Canyon) and fairly flat along the Glady Fork. US 33 is a 4 lane for a while, and has some climbing. The road stretch from Alpena to Glady is up and down… at Glady you get on the West Fork Rail Trail. The rail trail has a primitive feel to it. It can be shorted by camping along the Allegheny Trail S of 33.
You can come up with a different route back to BWSP.
Another option would to ride to Seneca Backcountry area which is basically NW of Spruce Knob, a popular place to camp is Judy Springs…. expect others (mostly backpackers) are there on weekends, but maybe empty during the week. There is also opportunities to primitive camp and there are free, dispersed car camping sites along the main FR. There are numerous single track trails to get to Judy Springs, but they may include some pushing… an easy way it is take the trail (old logging road) from south, which is ridable both directions. There is nice waterfall back in there.
Here is link:
http://www.bikepacking.net/forum/bikepacking/usa-wv-canaan-valley-area/ that you might find interesting… it won't be that green in September.
Here is some more info:
http://www.bikepacking.net/forum/routes/monongahela-national-forest-wv/ some it is out of date (written 10 years ago), but it gives you and idea.
I would recommend limiting the amount of single track on an overnighter if you want to cover much territory.
There are some neat loops that can be done in and about Canaan Valley--you could ride up to Roaring Plains and camp out at the top, at the end of the gated road... I've done that before.
You could also leave BWSP, go down the Blackwater Canyon to Hendricks and Parsons and then find a place to camp in the MNF W of Parsons, there is also some single track in there...next day, grind up 219 back to Thomas and back to BWSP.
Take a look at the links and think about what you do…. I can offer more info.
No matter what, that part of WV is awesome.
JHL99
Edit: Added Google Map Link