What brand and number rotor are you buying? It's harder than ever to get hold of good quality caps and rotors any more. You should be able to get hold of a rotor that will hold up over a reasonably long lifespan for you. Double-check the centre carbon contact in your cap, too; if that is burned up or faulty, it can destroy the rotor.
Grab a cup of coffee and read through
this (entire, long) thread. Proceed as recommended and I bet you won't have to think about your rotor for quite awhile, and other stuff will probably get better, too. Only departure from \6 practice as described in linked thread is that you
might wind up wanting a somewhat narrower business end of the rotor to account for the shorter spacing between adjacent cap terminals on a V8 application. Try it as directed and see how it works; you can always take a Dremel to the brass and narrow it a bit if that turns out to be needed.
