I would measure each time you re-tension the trampoline. Even with the corners epoxied, I would bet that an improperly tensioned tramp could pull it out of alignment.

The measurements are port bow to starboard rudder pin and opposite. Compare then pull the longer measurement closer with a line setup. Then tension the tramp with the line setup in place. Sometimes you will see a "spring back" effect and you will have to over tension the line setup, tension the tramp then release the line and as the frame settles in, it will end up more square.