Added Note: When programming a new tracker TNC, you should use herperterminal or a packet program other than APRS terminal mode. Try using PacTerm or some other program that does not have a start-up or shut-down routine, as using one, like HostMaster or APRS will change some of the necessary settings.
I've completed my "transportable tracker", and have employed the KISS methodology as much as possible.
This transportable tracker box consists of a dayglo orange plastic boaters box and tracking equipment. The box is not watertight, especially now, but it easily fit all the equipment necessary. I bought it for about $13 at a marine discount house.
The insides include a 12vdc rechargeable gel cell battery, an HTX-202 2m handheld radio, and a PacComm HandiPacket TNC. On the outside are the TripMate GPS, and antenna. I also mounted a power meter and DPDT switch, to change between internal and external power. The meter is checked by depressing a small momentary switch which you can't see in the picture. The main power switch turns the equipment on using either internal or external. There is no need for access to the inside components once the tracker is configured.
The above picture shows the components for my second tracker. It's mounted in a $5 plastic lunch box. It will also have a 12vdc internal battery, and hookup for external 12vdc on a cigarette lighter plug. The radio is another HTX-202, the TNC a Kantronics KPC-3, and finally my other TripMate GPS.
Both trackers will have one switch to turn on power to all the pieces, and external antenna mount. The case is designed to sit on the vehicle's floor. Padding inside will help keep the equipment stable, and somewhat protected.
The new TinyTrack III/4, OpenTracker, or TigerTronics TigerTrak (TX components of a TNC, w/freq carrier detect) is a great way to go when building a "portable" tracker. Marry these up with a lightweight vhf radio, like the Radio Shack HTX-202 and any one of a number of small serial-interfaced GPS's, and you have a great tracker.