This is my first design, made it on TinkerCad. Not pretty, but it works perfectly for me.
I purchased a microSD to SD extension because using the microSD slot on the Duplicator i3 is a pain and seems "delicate" to me. I purchased this from Amazon: (http://www.amazon.com/Manufacture-Sdhc-micro-Reader-Extension-Cable/dp/B0085GGO92)
Basically, it covers the cable and allows you to mount the SD adapter on the system. I connected it with a couple of drops of super glue. Hot glue would work just as well and it would be easier to remove. Its stable and does what it was made for.
Drawback is that it covers the USB port, which I never use.
You need an infill to support it, but its all hidden.