I'd go with strain-gaged washers. Here's a link to Transducer Techniques, but there are others out there as well -
LWO Series Load Cell @ Transducer Techniques
It will cost you 8 x $725 per container, but you can verify at any time the tension in each bolt, even long after it's left your facility. That may offer you some compliance benefit, or at the very least give you a competitive advantage. You could probably negotiate quantity discounts, and any loadcell manufacturer is more than happy to engineer a custom solution from custom materials, Inconel 718 for instance.