My kit came with one, which was discarded when I fitted a powervamp. Now back with a banner so have shoved a bit of tubing in and with replace with the official banner part!.
If no signs of corrosion anywhere the probably fine without it.
Now that is a very good point, Ian. Maybe I should think again....
Well, following Ian's comment I did think again.
I bought this cheapo vent hose from Alpha Batteries. The elbow was slightly too big, so I had to ream out the battery vent hole to 6.5mm. My battery is in the "old" location directly behind the ECU, so I needed to extend the hose to 730mm (from 500mm) to reach down below the chassis.