This combo does need support. By its nature, you'll be headed toward a moneyless deck, unless you pump Gold in there somehow (Market Square would do the trick). You'll at least need Villages to play more than one Death Cart per turn in the endgame, and probably +Buy to make use of the massive amounts of money you then generate. Worker's Village is thus the natural support to this combo.
For the IRL game, I used BoMs as Menageries for draw, but usually just once every other turn. I am remembering now that there was Grand Market and Peddler on the board. With those, the DC/Rats combo effectively doubles your coin output once you're running at max and ready to green, making it far easier to scoop up Colonies. And if you find your deck clogged too much with Rats, just use the DCs to pick up Duchies, since the Rats pile should be empty or near-empty anyway.