I am not very good at this.
I used c/k on the inside because it is somewhat lighter (uses less resin) and probably marginally stronger.
On the outside, I wish I had gone with glass. Kevlar fabric is just about impossible to sand. You sand the resin and the carbon out and then you're left with kevlar strands.
It makes a mess.
Using c/k instead of glass may have saved me a couple ounces, who knows.
I bought that stuff mainly to glass the tray back together strong (without gaining too much weight).
Since I already had it, that's what I used.