Disclaimer: This post was originally posted by Hero Member, mjb7843. This user is located in Zone 7, South NJ, Garden State. This was originally posted on August 23, 2013.
Some varieties are just prone to cracking. That said, bear in mind that plants take in water through their foliage as well as their roots. If you've had a lot of rain, the fruits can take on just so much water before they burst.
I know the Earthbox is not causing the cracking, and I doubt very much you've had anything to do with it either. There's not much you can do except pick the fruits as soon as they show signs of ripening, preferably before it rains... ideally, the cracks will not be too pronounced. Also, in the future try to select crack-resistant varieties and hope for a drier season.
Mickie