The first question I’d have is, how are you running 2.0RC and on what kind of hardware.
I found I was able to upgrade from 1.6 beta to a 3.0 version by just backing up the configuration, then restoring the configuration to a new 3.0 installation. If the hardware (or in my case virtual machine) doesn’t change, it might just work on the first try. Or at least if your network cards are identified in the same order, the device assignments (ETH00 etc) should be the same and your restored config should work.
Back up a config from the web interface; go to Setup, then Profiles. Select your profile and either backup or backup without logs. Install the new ZS, create a storage partition from Setup, Profiles, then restore your config to it.
This even seems to work if you’re migrating from a CD-based boot to a hard drive-based boot.