Water Proofing Canvas?

b.a. hart

Curious about Wooden Canoes
In past forums folks have identified great suppliers that have available "treated" canvas that may "resist" mildew or rot over the years and improve longevity.
My question is for those of us that already have canvas. Can we treat it ourselves with a preservative on the underside and yet use the filler on the outside? Treat both sides? Is this an OK practice and what brands/types might be selected? Thanks for your input! Bill
I use a plastic syringe to squirt copper naphthanate (sold as rope, canvas and wood preservative) on the canvas along the wale edge and stems before closing it all up.