This is simply not true. Wood has natural resistive aspects that actively prevent the breeding of bacteria, fungi, and mold. Keep in mind that the growing tree in nature has a strong incentive to evolve in a direction that will preserve and protect its wood from invasions of these exact types. Each of the various types of wood have various oils and aromatics within the wood itself that work to protect the wood. Magic-Flight does not need to add these—they are already there and are much better functionally than anything we could invent. Wood has to be exposed to wind, rain, and sunlight a fairly long time for bio-degrade to be possible in nature—years, typically. When we add sealants to the wood, it slows this process by a factor of 10x or 20X. Therefore, given the average of the exposure environments and this slowing, the wood in the Box should be able to last a hundred years or more—plenty long enough.
If you have any doubt of these facts, consider that there have been safety studies conducted on the relative merits of wood cutting boards in the kitchen vs Teflon ones. Although some vendors would prefer that you not know this, it is actually the case that Teflon cutting boards are far worse breeding grounds for bacteria and fungi than wood ones. Both types of cutting boards have tiny grooves in them (due to the action of the knife while in normal use)—grooves which can provide a home for bacteria and fungi. However, while the Teflon boards are inert, and thus do nothing to inhibit the growth of these cells, the natural oils in the wood make it much less likely that such cells can multiply and survive. These studies have shown that for most folk in most situations, wooden cutting boards are far safer. Only in industrial kitchens that regularly clean with chemical sterilization techniques can the disadvantage of Teflon be (temporarily) offset.
Keep in mind also that the need to "perfectly clean" the unit is purely a psychological one and/or a legal one—it is not (and never has been) a functional issue.