I use the "P +" system, too. Best thing. Be sure to use a Sharpie, though; the ink will smear if you use a regular pen.
I used to use the separate sheet of paper thing, and I still do keep my photocopies in case the actual passes get lost, but marking the passes themselves is so much easier.
BTW, if you have a safe deposit box, be sure to take the time to go down and put your partially-used Hoppers in it when you return from your trip. They are absolutely safe there, and easy to find for next time.