Substitue "from" for "as" and that is almost exactly how the Western Patrol Club formed.
Couple of people with Patrols having a chat at a popular spot... post on Patrol 4X4 Forum seeking EOI and advertising an informal meet up to appoint a mob to get it happening and... voila... our 4th Birthday was 2 months ago.
Having a lot of years experience in the world of Incorporated Associations if I may offer a word or three of advice.
Do NOT even go ANY further than EOI without incorporating.
Public Liability Insurance can be suprisingly affordable (expect a number around $20 to $40 per member depending) but is only a small part of the heartaches in setting up a Club.
A few IMHO's if I may...
I agree with Silver in that joining an existing 'local' Club is prob preferable.
I'd let the Forum be the Forum, proudly wack up a sticker or whatever if you wish.
Running a national club with state chapters will be a huge administrative task to comply with legislation etc so unless some very dedicated and knowledgeable people step up it will be tough.
I guarantee there will inevitably be a poo fight at some point between Forumites who don't want to be Clubbies and Clubbies who develop a sense of "ownership" of the Forum... sure the Mods can stamp it out but nobody wins if it happens.
It will be almost impossible to get a Club Conny that has the same objectives as the Forum, one is an association of equals and the other is a vision of an owner administered by appointed Mods.
Bottom Line (again IMHO)
If one was to try and do it I would advocate the best way is set up a Club as a totally seperate legal entity but with a memo of understanding between the Forum owner and the Club regards use of Letterhead, Logos, Forum Content etc etc. IE try and make the two as seamless as possible.
Me, I like it the way it is but no biggee and I have enough on my plate as a member of one Club