Without seeing a picture these sound like gel coat cracks, they are more common in the front and rear caps than on the sidewalls but can appear anywhere where the gel coat is thicker than .020. The surface looks fine leaving the show room but when a load is put on it such as a ladder load or vibratory load, small cracks appear but usually don't go into the FG substrate. Cracks emanating from screw holes are common because that is where the stress load is introduced into the laminate. Gel coat cracks can also be caused by heat (sun or engine heat) because the gel coat which is pure resin expands much more than the laminate it self. Bottom line is unless the cracks go into the FG it will not affect the structure.