Don't know what type of door latch you have, but a trick - we did on the Scamp
was to reverse the outside handle. Normally both the inside and outside handles point toward the hinge side, and you push down to open the door. The weight
of the handles may be enough to unlatch it when you hit a bump.
With the outside handle reversed it points the other way and counterbalances the inner handle. An added benefit is that if a stranger tries to open the door by pulling down, they will think it is locked. You will have to lift it.