H2 Enclosure
You can 3d print the following enclosure for your Portapack:
And the following magnetic cover:
If you do not own a 3d printer, you could use a service like https://www.weerg.com for a high quality print, or https://www.3dhubs.com/ for a low cost alternative.
Check the assembly.pdf from the case files for instructions.
You can easily place a small 8ohm 1.5W (14x21x5.5 mm) speaker inside. There is no holes in the case but it seems that the sound quality actually improves with the case: https://www.youtube.com/watch?v=XkaGV9muvbg
Check more details about the speaker wiring here.