Grace, I can't help you with the base, but I can help with the mounting (though may prefer not to hear it :-) ). Fans are required by code to use a box designed and listed for the purpose; it has the heavier duty support required. Any decent hardware store should carry them. The new box is easy to install, it's getting the old one out that's tough if you don't have access from above. Since this is a rental unit, you may technicly need an electrician to do the work.