Why didn't they bang on the walls?

It's hard for me to imagine a situation that I could be in where I needed to move so badly that I'd risk my life just to cross a border. For the three people in Men in the Sun life seems to have been almost meaningless without successfully being smuggled in to another country. Not only were they willing to sit inside a metal water tank during each checkpoint, in the end they were willing to die rather than be discovered. Granted, they may have been too weak due to the heat by the time they knew they were going to die but its still tragic that they'd rather die than bang the walls. It's also worth noting that the eldest of the three was good at keeping time without a watch so he would have known when too long an amount of time had passed.