It's a good idea to break it out into an external module anyway. That way you can test it more easily (in isolation, away from the rest of the application). There's Catalyst::Model::Adaptor to make this easier. From its description:
The idea is that you don't want your Catalyst model to be anything other than a line or two of glue. Using this module ensures that your Model classes are separate from your application and therefore are well-abstracted, reusable, and easily testable.
Right now there are too many modules on CPAN that are Catalyst-specific. Most of the models would be better written as a class that handles most of the functionality with just a bit of glue to make it work nicely with Catalyst. This module aims to make integrating your class with Catalyst trivial, so you won't have to do any extra work to make your model generic.