Dual Battery Set Up - Navara

My step father has been advised by an auto electrician that the only way he can have a dual battery system set up in his Nissan Navara STR Dual cab is if he was to install a snorkel, which will then give him enough room in the engine bay for the second battery, or mount the battery in the tray or undecarriage.

Is he getting the correct info from the auto electrician and if so, how have other Navara owners without snorkels installed a dual battery system into the vehicle.

Cheers in advance guys.