I'm planning on using the design shown in K1ZM's book to shunt feed my tower for 160M. Two questions: 1. He specifies using vacuum variable capacitors for the matching. Why those types? Can I use air variables? 2. He shows weatherproofing the matching stuff in a rubber (non metallic) enclosure. What if I use a metal box instead? Will the capacitors be affected by the metal enclosure? 73 Phil KB9CRY