When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
When I bought my Lund tri-fold,I asked that question specifically....I was told NOT to use Armour-All,or anything like WD-40.His reply was simply wash it,and do your best to keep it clean.
I get the impression that as long as its fairly pliable,flexible,and relatively clean its good to go.
I have followed his instructions,and so far(after 2 years) all is indeed well.