Trying to make the bottom of your kayak cosmetically durable is a losing battle with varnish since you will see every scratch through the varnish and an accumulation of scratches require revarnishing to protect the epoxy. If you want clarity and durability use extra layers of 4 oz eglass on the bottom. I wouldn't bother with Kevlar or other fabrics on the outside since compression strength is more valuable on the exterior than tensile strength. Save the cosmetic attention for the deck and let the hull do what it does, deal with landings.