[Formulajones]

To add, you at least need to have the small 1/8" or 3/16" vacuum line hooked to ported (switched) vacuum source for the switch to activate and purge/vent the tank. If not there will be no way to vent the tank and you'll have to find other means (ie vented gas cap or baffled vent etc...) or you'll have funky run and fuel delivery issues.

I guess it doesn't really matter whether you hook the vent hose from the canister to the engine or not, you mentioned just running the line open down below the frame. That works but would be smelly. As I mentioned there is no harm in hooking it up correctly. On my chevelle it T's into the PCV and then runs to a manifold vacuum PCV connection on the carb base plate (holley). I run an AFR gauge on it and it has no affect.
On my Firebird I believe this hose goes to the vent on the upper air horn of the Q-jet.