G'day broadside. Welcome to GPSPower. Interesting choice of nick, seeing as you'll need one of those if your mused "install" location is where i think it is ...
A 'conventional' GPS device isn't what you want [e.g. Garmin, TT] of course. You'd be likely referring to some kind of miniature GPS tracking device, similar to or of the type you use to track kids, pets etc. I wouldn't like to think about trying to stick even the smallest of those commercially available units 'back there' anyway ... brrr! I reckon the kidnappers might have a quick sift thru your 'leavings' anyway. As to whether one of those things would actually work 'inside', i really doubt it would get a proper fix or be able to TX it's locstat satisfactorily either from .. up there .. One way to find out, know any gentle proctologists with a sense of humour?
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Failing that, maybe buy some spook from MI5 a few drinks. I bet they've worked out how to do it.
Good luck Mate. Sorry for the levity, no offence taken i hope. I genuinely wish you success with this and a safe return from whatever hellhole you're heading off to.