Take a look at the Polyphaser site - www.polyphaser.com
They have technical articles and a very good book on
the subject. I think the book is called something
like "The Grounds for Lightning Protection" or something close. The most protection for the money
seems to come from using the appropriate ground radial straps tied to the tower base and using a single-point ground panel bulkhead feed-thru panel for coax and control cable entry with appropriate protectors.