The tape is insurance against an inadequate bond between the thin bulkhead and the hull. After tacking the bulkhead in place with a few dabs of thickened resin (and cure), I usually do these as one process, finishing the bulkhead/hull attachment with a good fillet of thickened epoxy, and then applying the tape while the resin is very wet. The tape gets some wetout from underneath, and I dab on more resin as needed to complete it. I don't know that the tape is essential, but I really want the bulkheads to remain attached. There is some hull flex in use, especially in surf, and strong bulkheads reduce that.