That said I would think Greg would be far better off if he could put mag mount antenna on the top of the train.

Nothin' doin'. Amtrak's Superliners are all-aluminum.

Here is a map of where I was able to make contact (circles with dots)
with an APRS/IGATE digipeater on my trip. More than I thought, not as
much as could be optimum. This was using a stock TH-D7A(G) with the
stock antenna:

http://www.littlebear.com/TrainAPRS1.jpg

Here is a picture of my room/shack with the getup. Sorry about the
resolution, I took it with my Motorola cell phone. Above my PowerBook
is the Kenwood TH-D7A(G), to its left are the two GPS' (Garmin M5 and
60CS). You can see the GPS antennas on the window to the left of the
GPS' too.

greg