with this engine as SkyLine should be convenient and functional forum!
I suggest this http://www.invisionpower.com/apps/board/
With the help of it you will get a lot more active users, it actually works!
here are some examples of these sites:
http://www.gamestart3d.com/forums/
http://www.leadwerks.com/werkspace/
I'm not saying that you need now goes, no, it was you in the future..