I have been told that it is "best" to install any plastic product within the mediam temperature range of your area due to the expansion and contraction characteristics of the material. As stated above, drill out your holes a fraction larger and do not torque down on the fasteners. Allow some room for movement but still keep them secure. Of course, the weather or temperature is never always at an optimum range, but by not installing them in 90+ or 40 deg. and under weather will help keep them from excessive strains of expansion and contraction.