RED Tunnel for UTM 2 UTM, where should i set QOS? On the RED int's or ext int?

I have a RED UTM 2 UTM tunnel and i need to use QOS, but with IPSEC or SSL tunnels i would set QOS on the ext interface.  Where do i set this with RED?  I need it to give priority for RDP traffic or VPN traffic itself.  If I set it on the RED interface will it also work against the EXT interface? i.e will i get priority across the whole lot?

Thanks

JK