npm installs not available in CasperJS

According to the CasperJS Documentation, I should just be able to install things through npm and then require them in my CasperJS scripts for use (since 1.1 apparently, and I'm using 1.1.0-beta3)

However, this doesn't work for me and I get the error "CasperError: Can't find module ModuleName", where I've tried read, underscore, readline, etc. And, they've all been installed using sudo npm install ModuleName.

Is there something I'm missing?

EDIT: For reference, this is related, but not identical, to my question here.