Is the immersion method safe to use on these cases? I know some classic Macs have metallic paint inside that reacts poorly to the immersion method. Is the metallic-looking coating in the IIsi case similar or is the plastic just grey inside?
I used the immersion method, and it caused much of the metallic paint on the inside of my IIsi to flake away. Personally, I don't mind that it went missing, but if you mind, I bet you could protect the inside of the case with some kind of clear-coat spray paint before retrobriting.
The metallic paint is there to reduce radio frequency interference generated by the IIsi, but with all the noise in the current environment from switching power supplies, etc, you may not notice any problems unless you are an amateur radio operator or you have one nearby. Looks like if it comes off and you want to replace it you could buy a half pint of "conductive shielding paint" for $40-$50.