Hi Richard,
Like the idea, but appreciate that you may need to enlist a helper or 2 to fill and/or move the filled boxes. A single row,ie stacked along the path would take approx 30 boxes,(375*30=11.25m) if in a ‘portrait’aspect*. They would require approx 1.7cu metres of growing medium, which could topsoil with a compost layer, 2″. It would be simply a need to bore perhaps 6 x1″ holes through the bottom of each box using a holesaw in a cordless drill. Permitting drainage and worms to migrate.This would potentially allow the boxes to be moved while full, albeit weighing perhaps 40 kilos each when full.Have you considered microporous hose which could be threaded through the row of boxes and connected to a butt or tap to trickle irrigate, possibly with a timer?
Possible drawbacks? Initially resource hungry in terms of labour, creating ideal home for slugs and snails below/between boxes.
Positives are many, easy to manage. One box per day? Scope for ‘square foot gardening’ to intensify planting/cropping. Good luck with this, please report progress
Regards
Cleansweep
* when viewed from the path