First off: The compatible SDHC cards for the 2Box module that I have used have required no formatting. It is best not to format your card. But for those that have a problem, or have mistakenly formatted cards using on board Windows or Mac formatting here is the formatting tool that you should use to reformat your cards:
https://www.sdcard.org/downloads/formatter_4/
Normally just do a Quick Format, Format Size Adjustment Off
32K is the cluster size used by the 2Box module.
Important reminder for those that have done the Card extender mod: Once you have done the Card extender mod you must use a card reader with your computer to do any of the functions you normally would do via usb connection from the module. You will no longer have access via the module's USB port. You will only screw up your SDHC card if you attempt to connect the module via USB after doing the mod. J