Here's some things I've put together for APRS.

If you want to put together a cheap antenna for portable APRS use here's a simple J-Pole design.  

These are the settings I use on my KPC-3 in my Mazda Navaho.   You can cut and paste this to you comm program and load it directly (after editing).

INT TERMINAL
MYCALL KD4BBM-12
ABAUD 4800
BTEXT KD4BBM Ray's Navajo SUV <rvaughan@gate.net>
BEACON EVERY 00:10:00 START 00:08:08
UNPROTO BEACON VIA WIDE,WIDE
GPSHEAD 1 $GPGLL
GPSHEAD 2 $GPGLL
GPSHEAD 3 $GPGLL
GPSHEAD 4 $GPGAA
LTP 1 APRS
LTP 2 APRS VIA RELAY,WIDE
LTP 3 APRS VIA RELAY,WIDE,WIDE
LTP 4 APRS VIA WIDE,WIDE
BLT 1 EVERY 00:00:47
BLT 2 EVERY 00:02:57
BLT 3 EVERY 00:06:27
BLT 4 EVERY 00:09:37
MON OFF
CD SOFTWARE
CMSG DISC
CTEXT Stand-Alone Tracker, Disconnecting. rvaughan@gate.net
BUDC +DGPS
BUD ON
INT GPS

Good luck with your APRS projects.