I like the tube rack. Looks good to me. I have been building furniture longer than I have been fly fishing.
One improvement might be to use a router to create circular divots for the bottom of the tube as well so the bottom of the tube stays put. You could also use two boards(Drill completely through the top board with a hole saw to make the space for the bottom of the tube. Leave the second board complete to create the base for the bottom of the tube to rest on.)
YOu could clamp the top board and bottom board s that would recieve holes at the same time on your drill press or even if you used a hand drill and a strandard hole saw.