Hey Dany. I think there is some conflation between sweat and water damage with the vive. To be specific what a lot of people put down to sweat damage, vive support reports as 'water damage', is almost certainly condensation damage i think.
Especially when used in a colder climate, and with a cover over the normally porous foam a temperature and humidity difference can form between the internal space in the hmd and the exterior environment. This causes condensation to form on the interior surfaces of the hmd where the cool environment is on the other side of the surface. I have observed this first hand with my vive in ireland during winter. While not an issue when it occurs on the sides of the hmd beside the strap locks (where i observed it directly and repeatedly) , if the same happened at the front of the hmd , the tracking sensors are close enough to the exterior shell that condensation formed there could contact and damage the pcb, which is what i think has been happening when looking at various peoples support images of 'water damage'.
This should be especially relevant / investigated given you are using the same tracking technology.
Ideally to prevent this from happening you need to be able to vent the moist hot air inside the unit so that the temperature and humidity outside and inside the unit remain the same and do so without allowing in light pollution.
While a fan could certainly aid this, i dont think that will be necessary if you have top and bottom ventilation you should get natural airflow of the hot air rising out of the unit and conversely drawing cool air into it as needed to maintain temperature balance.
At the very least i would highly suggest testing the 5k/ 8k at high activity levels in an increasingly cool environment for 45 mins to an hour at a time (audioshield would work well) in order to determine if there is a safe temperature range for operation without the formation of interior condensation. As long as people are aware of the issue they can take steps to mitigate it ( in my case i use an additional heater in the room in winter to minimise temp difference between inside and outside hmd to prevent the air inside the hmd reaching its dew point. .