I believe the mod was constructed with positive down in mind, battery vents from positive so that should be the part near the vent holes. There's no vent holes at the top. Maybe it wouldn't blow out the top but certainly blow out the side and over your fingers, eventually accompanied by some molten plastic or sharp shards of plastic.
That said, positive down brings its own risks, battery wraps cannot be damaged in any way or you'll get a hard short. If you ever manage to get something into those cutouts in the side of the mod by accident that would spell trouble, it could tear open the battery wrap.
So either way isn't a particularly good way to put the
batteries in... you'll have to make the decision on what you feel more comfortable with. If it was me I'd probably still go with positive up and count on my ninja reflexes
