only works on C:

[Paruccone]

an option should be available for it not to use C: drive for storage/temp.

manually setting $mainOSDrive doesn't help, script keeps referring to system drive here and there:```

The operation completed successfully.
Mounting Windows image. This may take a while.
ERROR: The system cannot find the file specified.
C:\tiny11\sources\install.wim: The system cannot find the file specified.

because of 
$env:SystemDrive being used later on instead of $mainOSDrive