why would you not want to use it? btw using a tracktrain for a door is a bad idea for two reasons:
* due to a weird bug in source, tracktrains don't move through the origins of path_tracks, but stop at the edge of the path_track box you see in hammer. hence a door wouldn't close all the way and your areaportal would be screwed up
* func_areaportal uses a linked door to work. if you use a tracktrain, you'd need to use OnPass outputs from the path_track to turn the areaportal on and off, which is a load of unnecessary work