I have an alpha delta DX20 which I am limited to mounting a certain way, as opposed to simply supporting the ends with the center in free space. I have a plumbing vent pipe which appears to be the old cast iron type near the center of the roof, a few feet down from the peak; to which I plan on mounting a vent pipe mount kit with a 5ft mast to support the center of the dipole. The ends will be tied down to eye hooks at the gables of the roof, again a few feet down from the peak due to landlord "concerns". I've read somewhere that the center support should be a non-conductive material, but I'm concerned if 5ft of pvc will hold up in winds. How much would using a standard metal mast in the center affect my SWR on transmit? It seems hard to find a solid answer to this question.