Living in New York, I'm probably a bit overly paranoid about leaving stuff attached to my bike. I strip all the loose stuff - blinkies, computer - when I have to park it outside. And I ride a fix which has next to nothing in terms of components to attract thieves.
I used a VETTAbox for a while, but despite being made of hard plastic, it still seems to be a bit flimsy and easy to jimmy. Don't know what the petty crime rate is like where you live but if I was planning on leaving my stuff unattended, it would have to be really secure. I see people locking up stuff inside their motorcycle and scooter boxes, I would think that option is more sturdy and secure than anything made for a bicycle.