Hi Charlie,
We are working on integration with APM-based autopilots, it should be in a beta stage in a couple of weeks.
Reach already outputs NMEA, but NMEA does not provide enough data for APM, so we decided to add a binary protocol to provide better integration. More information on this topic is available in another thread.
Reach can work in such environments, but it really depends on how satellites are visible in this area. If they are high then some trees and small buildings should be okay.