You could add some support to individual stems or put a wire fence around the plant. That is a fairly common thing to do with Hydrangea Annabelle that might help in this case.... until the stems have become strong/old enough and then support is no longer needed.

Mine never seem to get damaged. If I happen to be out there after a rain I might give them a gentle shake, but that's it. They aren't like peonies, which seem to explode from rain.

Mine had trouble the first year but after that it seemed to take care of itself. I live in the very rainy northwest. I caged one and did like Sue36 and just shook the water off the last one I bought. I think the nurserys grow them really fast so they don,t get have any strengh to the stems thier first year out in the real world conditions. It will also faint on you when its gets to hot. It will stop doing that after a year or two in the ground.