In the step by step instructions - see below
[In the Destination Folder area of the Setup Type dialog
box, verify that the Program Files location is set to a
valid local drive on each node (for example, C:\Program
Files\Microsoft SQL Server) and that the Data Files
location is set to the drive selected on the Cluster Disk
Selection dialog box. If you want to configure a specific
directory on the drive for the data, click the Browse
button. Click Next.]

Does this mean C:\ drive is a local drive to each server &
not a shared RAID drive. In other words do you have to
install SQL Server on the C: drive of both nodes?
Presumably the data files have to go on a shared drive
though?

Yes, the programs are installed on the local drives on
each node. The installer does it for you, so the same
local drive configuration must exist one each node.

All data files, including system DBs, go on the shared
disk array.