How should I design Mechanize & Nokogiri crawler functioality into my Rails app?

I am tring to build my first web crawler and scraper for one of the features within a rails app and I'd like some advice on how best to design it.

I'll use Mechanize to navigage pages and complete forms to submit then Nokogiri to scrape the data from the resulting served pages. My app will need to run these operations for various different urls each with differing form completion, submission data scrape requirements.

How would I be best to design/house/encapsulate such code to serve a rails app? Internal Model Controllers without views, rake tasks being called from exiting controllers, separate API?

Advice for a newbie appreciated. Thanks