Many Pros online do not trust Kerdi by itself an I have seen coutless examples or Red Guard, Hydro Ban and Aqua Defence used to reinforce the Kerdi Seams. In 12 years I have never once used Kerdi by itself without this extra protection.
I would bet that Laticrete gives you their blessing on this.
Why not got straight to the top. Ask Henry.
Henry B Rothberg <HBRothberg@laticrete.com>
Henry is a great guy and will tell you straight or point you in the right direction.