Sara, something that has increased my confidence and strength for standing up on climbs is going to indoor spinning classes.

Now, in many ways, standing up on a spin bike and on a real bike outdoors bear no resemblance. However, doing some really hard spinning workouts with LOTS of out of the saddle time has increased an aspect of my leg strength that is different than seated hard work has.

I am noticing that although outdoor standing climbing is still something I need to work on, especially for coordination, changing gears while standing, etc, I am much more able to handle the wobbles and errors in gearing because my legs and upper body are much more used to it.

Good luck!