Here is a front Box to attach to your Ender 3 to give it a place to hold your SD card converter to use full size SD cards, and to add a light switch.

You can also find my LED light bar for Ender 3 here: https://www.thingiverse.com/thing:3292889

I made a slot on top to collect your extra SD cards.

You can print face down with no supports if you use the file: Ender3BoxV2wSupp.STL
I have created a support piece to be removed and thrown away. It’s the small rectangular box with the angled slit for prying located under the box on the double screw side.

If you print with 0.2 layer height, 2 walls, and 10% infill, you will get nice results.

Or print face down adding your own limited supports (in left area around mounting screws) using this file: Ender3BoxV2noSupp.STL

You will need some longer screws to mount it:
2 M5 x 15 long
and 1 M3 x 8 long

You can get the switch here: https://www.amazon.com/gp/product/B071DNCFW1/ref=as_li_ss_tl?ie=UTF8&psc=1&linkCode=sl1&tag=petersolomond-20&linkId=8edeb170b6356125f4ee49d6387dd3df&language=en_US (affiliate link)
and
the mini to full size SD card Converter here: https://www.amazon.com/gp/product/B071DNCFW1/ref=as_li_ss_tl?ie=UTF8&psc=1&linkCode=sl1&tag=petersolomond-20&linkId=8edeb170b6356125f4ee49d6387dd3df&language=en_US (affiliate link)

Mounting is fairly straight forward, just push fit the SD Card Converter ( I like to accordion fold the cable and lightly glue each layer with a drop of hot glue), press fit switch, remove your two front screws from the lower left side of the machine and the bottom small screw from the bottom of the Mother Board enclosure. Wire up, fit the cover, and screw it in place. I even left some cable passage holes on Right side incase you plan on using a raspberry pi or using the micro USB.

https://youtu.be/uGz_VD3Hgv8

Updates: V2 added a few cable passages underneath, modified angle of SD compartment to be a bit more upright. Made SD converter stick out 5 mms for easier grip on card.

I hope you like this, if so post your makes, and let me know in the comments!