My ScreenOS is rusty, but IIRC, it's easier to use the /64 tunnel network on the tunnel, and the /64 assigned network on ethernet1.
Also, I don't think that 'set ipv6 mode host' is correct on the tunnel interface; Ithink that needs to be set on a routed port.
My old 5GT (5XT) is in a box somewhere and had a working config on it. I can dig it out if needed.
Also IIRC, the IPv6 guide for ScreenOS was pretty good. After setting a variable, rebooting, and a few cryptic commands, everything else was just like IPv4 in ScreenOS: address book entries, policies written from zone to zone, etc.http://www.juniper.net/techpubs/software/screenos/screenos6.3.0/630_ce_Routing.pdfhttp://www.juniper.net/techpubs/software/screenos/screenos6.3.0/630_ce_Dual_Stack_IPv6.pdf