Vented Gads Cap

[magwakeenercew2jh]

If I have a vented tank, do I need a vented gas cap?

The vent is clear and open.

As most know, the vent line is a hard line that runs from the top of the tank (behind the passenger's head) up the passenger's side corner,
looping back down and then exiting thru the floor. From there, after a short length of rubber hose, it twins up with the hard fuel "supply line" along
the frame rail.......until the supply line branches off to the fuel pump at the front of the frame. I believe that the vent tube originally went into a charcoal filter...
I just have mine open pointing toward the right and into the atmosphere.

I finally found an unvented cap that keeps the gas from sloshing out of the fuel filler hole. So, the question remains...Does this set up require a vented cap to avoid
some kind of vacuum-caused gas-flow problem?

Or do I just happily run with a sealed filler, relying on the vent to keep everything flowing properly?

Or do I need to know something else that I'm missing?