You use a circular needle for large things like afghans because regular needles won't hold all those stitches. You use the circs like straights on this kind of project. Finish the row, then turn the whole thing around to work back the other way. You won't be joining the stitches to knit in a tube.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry