I baste all three layers at once as well. I usually pin baste, sometimes thread baste. I work on my cutting table using binder clips to hold all the layers in place. For stripes, I would probably leave one at each top corner and one at each bottom corner to hold the stripes straight until I got the whole thing basted. I normally clip backing; lay batting and smooth it out then use the same clips to hold those 2 layers together and repeat for the top.