The main risk is with stacked batteries, and using cheap batteries, and with no multimeter. Unless you are doing 6v on the SB then you are probably not in the danger zone.
It can't hurt to drill vents, of course.
To be honest, once a battery starts to go, it will need need slots not holes to vent all the gas. The main use of vent holes is to tell you what is happening, because in every report of an incident I know of, where there were vents, gas was ejected strongly for a couple of seconds before the whole thing went up. You get two seconds to sling it. Otherwise the only thing that will work is a bottom section that blows off first.
We're probably talking about a cubic metre or more of gas being produced in a few seconds. It just can't get out of a couple of small holes fast enough. The vent holes will jet hot gas onto your hand and you'll sling it. Natural reaction. It's what has happened in several of the reports. Then it blows.