When i ship out collector / trading cards, common practice is to tape the card in between 2 slabs of cardboard to prevent bending (this ofcourse being inside of a sleeve / top loader plastic liner). Usually the protective case is taped to the cardboard with blue painter tape. It doesnt leave residue behind on the cardboard nor the plastic holder
I have bought ink-on-calfskin art and had it shipped to me, the artist wrapped it in parchment paper and taped the parchment envelope to the inside of a cardboard sandwich.
But for SD cards, I would expect affixing it to the inside of a cardboard sandwich with masking / painter's tape to be perfectly adequate, though not by any means pretty.
Here is one I’ve found for example [0], although a double sided one might “look more professional”.
[0]: https://www.mcmaster.com/product/1756N101