Any vapour in a battery pack enclosure has the ability to condense if there is a change in a surface temperature. Condensation can then gather and result in corrosion or electrical shorts. Larger battery packs often have a breather to regulate the pressure differential inside to outside and limit the pack deformation and seal failure. However, a breather brings air exchange and possibility of higher humidity inside the battery enclosure.
It is a challenge to understand how much condensation there might be and how that should be dealt with.
Tesla Model 3 Cell Busbar Failures
A failure mode of this design when the cells are arranged to point downwards is that condensation collects on the cells and then runs down to the wire bond connection on the shoulder of the cell. This can corrode the electrical connection on the cell.
Creepage and Clearance
High voltage circuits can discharge across a gap, the gap can be through the air or across a surface. Minimum creepage and clearance distances for a given working voltage and pollution degree are set out in IEC 60664-1 and ISO 21498; use the creepage and clearance calculator on this site for indicative minimum figures based on those tables.