RDS 2012 R2

[badders]

I'm trying to setup RDS on server 2012 r2, a quick test install using two servers worked fine and was easy to setup, I'm now trying an advanced install involving 6 servers with two in a DMZ (gateway and web access). We have smoothwall as our firewall and bridging rules have been created to allow the two DMZ serves to join the domain. I'm using the RD licence server to manage all the other servers in the RDS collection, this is fin for local network servers but trying to add roles to the DMZ servers keeps failing. Has anybody else tried setting up RDS in a similar way? I want to make it as secure as I can which is why I'm using the DMZ.