Our boxes are made from ABS plastic and small cracks maybe fixed using an ABS cement. You can also try using a product made by Gemini Materials called Patch and Repair. Here is a LINK to that product.
Neither of these options will return your box back to "new" condition and are not guaranteed by Yakima.
For further information you can contact us here, or by phone at 888-925-4621 M-F from 7 to 4 PT