Those mantraps are vicious. I ran for quite a while from them and then they ended up waiting for me outside of the gates of ishad'nah. I managed to run past them ( I had to drop the graphics quality so the game wouldn't be so jerky, as I kept getting hung up in trees while the mantraps made mincemeat of me). I was running by the burned out house with the mantraps hot on my trail.
After reaching the burned out house I headed West and then ducked north up a little trail and waited at the end. Surprise surprise the mantraps got hung up at the entrance to the little trail and I just stood back and cast flamedrop at them from a distance. I think the mantraps were to big to follow me through. I'm not sure if it can work everytime or if I just got lucky, but it'd be worth a shot for those that are still trying to make mantrap-salads. Happy hunting! :']

Should work every time as you cannot ride the horse through here either.