No arguing with what's laying around, David! I thought about making a version of the PR clamp when I saw yours but the clamps I have are hold downs and the other thing (wrench) which was just laying around worked so well, I opted for lazy. A plier or lever or cam clamp with the half-round jaws will also work; think Jim Legg put up a picture of his a while back. The older hand-cranked roll crimpers are self-contained and, although not designed with plastic hulls in mind, do the job every bit as good as any roll crimper head currently on the market. For those who have them or can find them, I wouldn't allow one to moulder away on the theory that it's old hat.
jack