@kiniki
In my experience, all hard drive cases, including the small laptop drives used in Amiga 1200s, are in direct contact with the carrier/chassis/earth of the computer. Talk of insulating them sounds like nonsense to me. How would you insulate the screws going into the case sides?
If I'm wrong, I'm sure someone will correct me.
@orange
I suspect that the A1200 HD carrier is a standard laptop IDE drive holder. If not it can't be very different and I'm sure you can adapt it to do the job. You often see these going for a few pounds on eBay.
Chgeers,
JaX