Raspberry Pi 2,3,3b+ sleeve case

I really liked the original design by walter, but it his case did't fit my raspberry pi 3 with heatsink and did not have gpio access. So I decided to remix it.
For the bottom part use the one provided by walter (https://www.thingiverse.com/download:1490773)

To obtain the grid effect I used the infill (as suggested by walter).
- Grid infill 15%
- No top/bottom layers
- 5 perimeters