First, Cambronne, I finally found a Payless store that at least knew about the Cross-Trekker Land/Water model you discussed about a month ago. You must have gotten one of the last pairs as that model was out last summer and, alas, is no longer. So I got the bright idea of waterproofing a pair of inexpensive lightweight leather/nylon upper hiking boots. That led me to passing along to the group some info about a brand of waterproofing products called Nikwax.
Nikwax makes a series of products for different waterproofing applications. There are wash-in products for cotton apparel (Cotton Proof), down-insulated apparel (Down Proof), synthetics and sythetic-insulated apparel (Polar Proof); brush-ons for leather only footwear, leather and fabric footwear; spray ons for things that can't be washed; washing products for preparing apparel for waterproofing and maintaining the waterproofing. The wash in products do not mat insulation. They work by treating the individual fibers. So piles and downs stay fluffy, but won't absorb water later so they maintain their insulating properties.
I have used the leather footwear as well as the leather/fabric footwear products, Cotton Proof, Polar Proof, and the Tech Wash prepration/washing produt. The Polar Proof can turn an inexpensive nylon windbreaker into a rain jacket. Water beads up and runs right off, but the fabric is not "coated", remaining pretty breathable.
The only problem with Nikwax is finding it. Your best bet is a well-equipped outdoor store. I am lucky to have one nearby that does stock. Nikwax.com has a dealer locator, but it doesn't seem to work. The website does have extensive instructions/guidance about how the products work and how to get best results.
By the way, I am not on commission or anything. I just like this stuff, and I havent't seen anything even close in terms of performance.