Hi People you are all overlooking the RF problem, in the first place all shipping containers is build with metal and without an external antenna no GPS receiver module will be able to log on to the satellites and a GPS needs to log on to at least three satellites to compute its location, second how is the unit going to send it's location out to the GSM network? for a test take your cell phone into one of this containers or in the back of a truck close the door an try to use your cell phone, it just don't work. and if the unit have to send the data via satellite to the control centre it need a transmitter of at least 10 watt and a propper antenna, and what about power supply? battery? how long will it last and how big will the battery be? so forget it anybody who tell jou it can be done talk nonsense. I did a tracking project for game in the Kruger National Park in South Africa and I know what I'm talking about.
I am 1.3 Km from my nearest GSM tower and in line of site with a 10 element Yagi external antenna on my 3G modem and the best signal I can get is 4/5 so GSM is totally out.