When you have serviced your transmission, did you notice anything unusual in the pan (you have serviced on regular basis, yes?)? If you have never had any symptoms (like slipping or irregular shifting), and you have serviced regular without any indication of problems and have not overheated trans, then keep your money for emergencies and enjoy your trip.
I was considering doing basically what you are when my daughter was switching coasts every 3 months (she worked on east coast and went to college on west, switching every 3 months). I did not want her truck to have transmission problems so considered changing it proactively, but ended up just servicing it. It has run fine for another 50k miles so far with no problems.
