UPDATE: I finally found a SATA data cable which is sufficiently low-profile enough at the drive connection end so as to allow me to install a secondary 3.5" HDD into the 30L chassis and let me close/lock the side panel. German company Kabel Direkt had a sleeved, braided cable in 60cm length that fits near perfectly (I'd have opted for the 30cm one instead, but it was out of stock)
Anyway, here's their product page, should anyone else need to install a 3.5" HDD drive into the very neat confines of the 30L's drive carriages.
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