I work PT for a painting contractor. He just has the factory divider wall with the ventilation slots covered with plexiglass. Some type of ventilation is always going and I rarely smell anything inside. We've hauled my motorcycle with a gas can and I didn't smell anything. However, when stopped, in summer months, I'd think gas fumes could get quite strong. You may investigate gas can holders bolted to the back doors. This would alleviate having to remove anything to open the rear doors. I was thinking I saw where one of the rack manufacturers on the site offer gas can holders that bolt to enclosed trailer walls. Those may work, in your case.