Systematic way to upgrade from attachment_fu to carrierwave?

Question

I'm working on upgrading an app to Rails 3, and attachment_fu is broken so I'm moving to carrierwave. Is there a systematic process that I can go through to upgrade from attachment_fu to carrierwave? Or a tutorial for it? Right now, I'm more interested in getting everything on the database end right. I'm using the filesystem store option for attachment_fu and carrierwave.

I've found a module, UploaderFu from http://ruby.simapse.com/2011/03/migrate-attachmentfu-to-carrierwave.html that tells carrierwave to use the same directories and filenames as attachment_fu. But it's not the entire answer, just part of it.

For example, in the db, I have a UserImage model, with :filename, :content_type, :size, :width, :height, and :user_id attributes. I added a :user_avatar column, and the following to my model

attr_accessible :user_avatar
mount_uploader :user_avatar, UserAvatarUploader

What exactly gets stored in :user_avatar. Is it just the filename? or something else? Do I just need to write a migration to move the data in :filename (stored like "hello_world.png") to :user_avatar? If that's the case I should just use the original :filename instead of creating a :user_avatar column, right?