Go to Home Depot, get what I call hand rail flanges that have female 1/2 inch pipe thread. 2 of those, 2 sections of 1/2 inch black iron or galvanized pipe cut to 20 inches, 2 90 degree elbows. Put that together, mount to deck where you want it. The measure for a price of threaded pipe to fit between them. Remove one flange and assemble. Then get driftmaster clamps and holders and your set.