I've just had a conversation about this thread with a friend who uses radio trackers on small wildlife. He offered the following comments.
Trackers of the sort that the vet was using on the raptors that I described (that can be picked up by both handheld antennae and satellites) need a whip aerial about 8" (200mm) long. They get by with a small solar panel ~50mm (2") square and minimise battery size and use by only transmitting in daylight. Not much use for instrument cases. I'd say. And the satellite fees (charged daily) add up to the order of thousands of dollars. An instrument would need to be very valuable to make it cost effective, even if it worked.
On top of that, anything that uses satellite tracking needs to be in the open air with minimal tree cover; again, not much use for instrument cases. The system used for tracking trucks is used only on demand (a signal from HQ causes a transponder in the vehicle to respond, on request and usually at scheduled times; again, not much use for instrument cases.
He did mention there is a Finnish system (not available in Oz) that enables mobile phones to be tracked positionally; this is separate from any GPS function the phone might have. Such GPS functions require the receiver being in the open air but the cellphone towers triangulate the position of any cellphone that is both turned on and within range. Such systems don't require the instrument case to be in the open but would require enough battery grunt in the phone for it to last any length of time.