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You can get basic caddies really cheap.
When I asked about them previously lots of people said they were unstable and unreliable. But that is on the assumption that you're using them like a normal external HD. My use case sounds similar to yours - wanted to access the information initially after an SSD upgrade, then after store them in a neat and protective manner just in case. Clear plastic ones are easier to write on and allow you to see through to the HD lable - just in case you do it for more than one.
+duncs +hippy
A SSD does not directly expose its storage blocks to the OS, only an abstraction to allow for wear levelling, so you should use the manufacturer's 'secure erase' tool. There might be one in the manufacturer's GUI toolkit, or something on their website that runs from DOS/USB.