Don't forget to maintain the temperature while carrying out the test. The material will behave differently when subjected to impacts on different temperatures.
Also, if the part you are experimenting on is the outside surface in contact with the air, then also don't forget to put on the necessary paint or any other surface coating that is originally used on it. This can also create a difference.
After cutting out the necessary specimens, make sure that the cuts are done gently and the cutted faces are smoothened enough to mimic the real life structure. The reason being after the cut out, the amount of pre-present cracks in the structure can increase and may make it more vulnerable to fracture than what can be expected in reality.
Since you are trying to model hail by dropping weights, you have to ensure that the weights has somewhat the same Elastic Modulus and rigidity as the hails. The reason being, if the weights are more rigid, then the cracks or even fracture can appear on the composite sample while it may not the case when hail of same weight is dropped on it. (Since in the situation of impact where drop weight is more rigid than a hail, all of the energy during impact will be taken by the composite sample).