Trunk splitting is an annoying cosmetic problem with trees of any size.
It has no effect on water uptake, needle retention, or anything else except that it looks peculiar to the costomer. Best prevention comes in keeping the trunks from over-drying by storage in the shade, watering them, and also by cutting the bottom strings quickly and standing them upright. The strings in effect pull the outer portion of the limbs inward toward the trunk while at the same time pulling the base of the limbs outward from the trunk exerting pressure to pull the trunk apart. The weight of the trees stacked on each other in storage will add separation stress at the lower trunk. Therefore anything that can be done to keep the trunk hydrated and reduce the pulling stress on the trunk will reduce the splitting. Reasurance to the the customer can be made with confidence.