Many good places to ride, depends what you are looking for.  Three places in Western PA that border and ride the Alleghney National Forest and are privately owned.  You can bring your own horses, join their organized week long rides or do your own thing.  Check out the Flying W Ranch, Cook Forest Scenic Ride and Hickory Creek Ranch, all have websites.  The first two can definitely accommodate a weeks' worth of riding.  I am not as familiar with Hickory Creek but have heard that it is a nice place. Also Big Lick Campground in Bennezette(a little more east) offers camping for horses and accommodates big rigs and is famous for being able to see the Elk herds.  There is also camping available in many State Parks and State Forest, some free & some a minimal charge.  Check with the DCNR (Dept of Conservation & Natural Resources) at http://www.dcnr.state.pa.us. Also Carolyn Cook, a good friend of mine, published two books on trails in PA  "Ride Pennsylvania HorseTrails", one covering the eastern part of the state and the other the western part of the state.  Her book gives locations, miles of trails, contact info for maps, nearby vet info, etc. and would be extremely helpful if you decide to ride an area on your own.  We live in Eastern PA (too conjested) but have land in Western PA bordering the Alleghney National Forest and bought the land because we had done week long rides at both the Flying W and Cook's Forest and enjoyed the area so much.  Please feel free to send me PM if I can be of any further help.