Do you need to get the extension for the load warrior basket in order to mount a snowboard rack in the basket??

Yes. The rack as it is measures 44 x 39 x 6.5 inches, with the extensions, it adds 18" to be 62” x 39” x 6.5". 62"= 157.48cm. So if you're board is 157 cm or smaller, go for it. You could possibly add two sections to be 80"/203cm but that's almost 7 ft and probably longer than most roofs. If carrying a snowboard longer than 157cm is your main concern, just get a cargo box, you can throw all your winter and summer gear up there as well. http://ep.yimg.com/ca/I/orsracksdirect_2108_11248510