does anyone know how to wire an external thermometer to an A/C ?

It would have to handle the wattage of an a/c, that chinese one looks like it may not handle much at all. Get one like this that can take that load, i think that one would blow its load bro.

The Tstat I posted says in the description that is for portable a/c or heaters so I imagine it is rated with enough amps to carry the load and would be fine. I would confirm the rated amps on the t-stat to match or exceed your portable unit which is located on the side of it before you make the purchase as a precaution. Mine are 28 L.R.A "start up amps and 7.5 amps load "running amps" so it would need atleast a 30 amp t-stat to be safe. But Buds pointed out a very important factor I left out.

The pic above looks like it has a 208/230 outlet on it (3 prong w/ground), its def not 120v outlet so it wouldnt work. But is a very important factor I didnt point out.

so ive worked in HVAC for 4-5 summers now. your best/cheapest bet would probably be just to install the thermostat in the room and do a little research or ask a friend with knowledge as how to wire it to the AC unit. im assuming you got a local cooling unit for the tent, right?
i cant effectively communicate to you how to install it over this, but ill help out. the 4 wires that leave the thermostat run off a 24V power supply (the red wire). the others control the fan (green), cooling (yellow), and the common is brown. the white controls heat so you can ignore it. you'll have to figure a way to wire these around, sorry i couldnt help much. whats the current setup for the thing?

thank you for all of the input. and my bad for calling it a thermometer. luckily my ac turns back on after i uplug it and plug it back in so im going to get what krazy80 suggested.