Why not ask "10-Tenths" if they are prepared to host the clubmans forum, as a private forum, as part of their site. It what SR & GT, 360MRC and CSCC do. I arranged for the latter.
You get the benefit of them running things professionally & you can dictate who joins the forum or doesn't. For eg, I administer all the CSCC forum admissions & the club decided that it would remain a members only board. 10-Tenths are keen to encourage the use of their general forums and will sometimes agree to host a club forum for free, if they think that they will attract a number of new members to the rest of their site.
General discussion about clubmans racing can still be stimulated on the normal elemants of the 10-Tenths forums such as under, "national and club" or Historic or sportscar & GT etc, as relevant. This is where newcomers can be pointed to, to ask for info & its where your own members can pop up & contribute to in order to market the club with contributions that are, shall we say, less controversial than those that may appear on the club only bit.