@hsmade

I can't say what the container is or the hardware inside but the hardware was never designed to have any transmitter/receivers inside the steel container. These are also old hardware devices, electronic boards would have been expected to be shielded from the steel surround and not have gps trackers inside it. i think they use the cellular network for transmitting and i suspect that after they moved the antennae to outside the casing it's interfering with other pieces of hardware. woe is me trying to prove this though.

gsm can cause a lot of interference, even when the other hardware is shielded.

I'm 100% sure the GPS part is not causing your problem, but the tracker probably had GSM or some other wireless system to send out its position to a server.

Get an RF meter (can be found for about $100) to see if the tracker is sending anything. I have one of a company called Cornet: http://www.cornetmicro.com/

Or just 'can' the 'other board' and attach it to the container so it has a decent earth connection