If there is no sheetmetal rear firewall, a sealed box vented to the outside is needed. The Moroso box works great. Box or not, a rear mounted battery needs to be held down by minimum of 2 3/8" studs or bolts to a framerail or framerail mounted tabs/brackets. The box or battery tray can be attached to the floor however you like. Battery hold downs need to go through to the frame.