... but how can I make forum be based on a different template than page.ss ????
I've tried making the forum code exend my FullPage model,
but it's not the model, I need to inherit the view, and not cracked it yet
Sorry - am an old style C programmer and this inheritance lark is all way too modern LOL
Templates are loading by hierarchy. The Forum template is nested inside Page.ss because it is in the layout folder. If you create a Forum.ss template in /themes/yourtheme/template/ (rather than layout) then it will use this rather than your Page.ss. But note you would have to create 3 page templates at the top level - Forum.ss, ForumHolder.ss and ForumMemberProfile.ss if you wanted full theme coverage.
The other option is to directly edit the Forum PHP code so that it extends your FullPage class rather than Page which is a bit hacky but easy.
Ideally you wouldn't have page types which simply control things like layout, design and instead have checkboxes or modes on the default Page.php which trigger design / layout functionality.