You can browse to TVH on your IceBox and change the recording location there.
http://[IceBox IP]:9981
Go into Configuration -> Recording -> (Default Profile) and change the "Storage path" under the "Filesystem Settings" to the location of your external HDD.
If you don't see that option, go into Config->General and set your "Default view level" to 'Expert".
http://[IceBox IP]:9981
Go into Configuration -> Recording -> (Default Profile) and change the "Storage path" under the "Filesystem Settings" to the location of your external HDD.
If you don't see that option, go into Config->General and set your "Default view level" to 'Expert".