[Zope] Programmatically setting default perms for products

Hello ... I am writing a disk-based product, and while I've set what permissions are required for various tasks using __ac_permissions__, what I really would like to do at this point is describe a set of default permissions for a newly created instance of my product (for instance, I want to set certain folders contained within to *not* acquire permissions, I'd like to set certain things to requrie authorized/owner/etc permissions, etc). I've looked around (perhaps I'm not asking the write questions to google and such) and have yet to find something that describes this. I'm assuming this is possible (perhaps it isn't, and that's why I can't find anything) - any hints? Thanks -J