I see so many people seem to mount wooden slats to the metal frame of the van and THEN attach their walls to those wooden slats. But if the slats are anchored by the metal frame, then could you just not attach the wall directly to the metal frame and save some space? And a step and some money and weight? Wouldn't the metal be more secure than the wood? I get making space for insulation, but the walls certainly are deep enough to start.