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I have been using the 4" pvc pipe setup for years now. There are no sharp edges to wear the tarp. Use one 10 foot section to run front to back. Connect a 90 degree elbow to each end facing down. Cut another 10 foot section in half to go to the floor . Where the two halfs touch the floor you use the pvc flanges that look like pedistal seat bases. Screw the bases to a piece of plywood for stability. Secure this frame with rope going over the sides of the boat. It costs about 40+ dollars to make but lasts for years. After the tarp is secured with bungee cords it looks like an army pup tent and can be taken off quickly to use the boat off season. Depending on what is in your boat you may have to make one of the upright pipes longer or shorter than the other. I have my 13' and my 16' covered with the same set-up. My 21 uses the same thing but needs a piece of wood duck taped to the front part to reach the front of the boat because the 10' pvc is not long enough for a 21' boat.
I know two people who carefully cut there shrink wrap off and get 3 years out of it and both of them have t-tops. They store the shrink wrap indoors so it does not get as much sun damage.