SSD Heatsink(s) / Cooler(s) in the market that fits in our Mac Mini Dock perfectly (should you decide to get an extra heatsink)

Sorry for the late reply, I missed this one, Olli. ^^' Well, if you're using a SATA drive too, then we'd recommend you closing the bottom case. If you're just using the NVMe SSD expansion slot, then it'd be just fine to keep the bottom case opened. However, should you decide to close it, in case you lose it. Please have the heat dissipation silica gel pad be sandwiched in between the inner part of the bottom case and the top of the heatsink, if space left is allowed. If not, it'd still be fine. =)