I just installed the basecamp update and was very pleased with the new implementation of the trip planner. It will now create hiking routes along marked trails on the map by just entering a start and end point (I used stored waypoints), much the same way it can calculate a street route. Activity needs to be set to hiking for it to work.
I might have been doing it incorrectly in the past, but the only way I could figure out how to do this was to draw tracks by hand, which was maddening.
You access the Trip under the Route menu on the device.