Commercial potato chips keep for a long time, in a sealed bag. Often they contain no preservative other than salt. They are sometimes "packaged in a protective atmosphere" - that is, the gas in the bag isn't normal air - but I suspect that treatment is reserved for the higher end of the market.
If commercial chip manufacturers can make them last months -- and have achieved this for at least half a century -- then you can make them last a week in your kitchen. I think your customers can reasonably expect "home made potato chips" to be at most a week old.
Try storing them in airtight containers. Lots of smallish ones, so you're not constantly opening one big tub, letting more and more moisture in. That may be good enough. If not, consider popping a silica gel moisture-absorbing sachet into each container before sealing.
One thing I'd add; commercially made potato chips are made to very high standards. There are some foods that demand to be freshly prepared in the kitchen. I'm not sure you can better a premium brand commercial potato chip, in your own kitchen.