The hinge loads on a pull-pull system are not all that different than that of a single push rod system. When a pull-pull system is activated, there is a pull on essentially one side only, the same as when a single push rod system is pulled. The only difference is that the pull-pull system will have some forward pull on the rudder all the time. With film hinges, this thrust load (tension) is absorbed by the leading edge of the rudder pressing against the back of the vertical stab. For this, I recommend leaving the trailing edge of the vertical stabilizer somewhat flat and rounding the leading edge of the rudder so it has a surface on which to "roll" as the rudder is deflected.