For SC, these holes or provision marking for holes?
We should have the same box for DC/EC, we cannot have in these versions. (Unless we use the method of bracket shown below - Bracket A)
If we use this kind of fixation provision, I would prefer to use your original plan of "tie-down hook" fixation, as current generation and same as your 'Concept fitting Side Utility Box Prototype'., see screenshot of bracket.