Waterproofing (again)

[MrKawfey]

Looking for some feedback on waterproofing. I know there are some old threads, but I figured there are enough new opinions to make it worth discussing again.

I have several items I would like to waterproof or re-waterproof. In the past I have had only minimal short term success with store bought sprays. I saw a couple of videos on YouTube showing silicone RTV thinned with Naptha or mineral spirits and then soaking items in a bucket. I think this might work well for a couple of stuff sacks that I have that were never waterproof in the first place. I can see how the mixture would wick into the fabric and seal it well.

With previously coated material, I'm not so sure. I'm a bit worried that I would be mostly adding an exterior coating that would easily flake off. In addition to not wicking in, nothing really sticks to silicone, including silicone.

I am also a bit concerned about the solvents attacking the synthetic materials. Canvas and cotton can handle it fine, but I'm not sure about sil-nylon or polyurethane.

Any thoughts?