Modules can have their own saved variables independently from a main addon. If you do this, treat them just like any other addon.
On the other hand, if you want modules to plug into a main addon's saved variables, you would use the namespace method.
After a lot of trial, error, and asking questions, I got the second method to work in SmartRes2 and SmartRes2_Chat. Both addons are no longer maintained, but the code to show you namespace and modules should still work as an example.