In my Experience the draytek v2820VSn with Draytek 120 for Dual WAN, works best on firmware 3.3.3 anything higher and I ended up with port forward issues on WAN2 for example Webserver port 80 not reliable most days dead website.

My system port forwards 7 camera's , XDove mail server , webserver ( QNAP ) , WebServer ( WHS ) , Webserver ( Smart Monitor ), Download server, FTP , and so many more