Installation of Victron DC/DC 30Amp charger

As advice by Victron expert (pvfarnell) I’m going to install Isolated DC/DC 30 Amp charger on my fishing boat. However I have limited room in batteries compartment.
Question: How critical is the distance between charger and the battery?
What’s recommendation in the wire gauge?

The manual will include details on wire size, but if the run is short 6mm2 will be OK. The units can get hot so spacing and ventilation are important.

Thank you!