Would this work?

Buy a section of 3/4" ID Schedule 40 PVC at your Home Depot or Lowe's local home center, make it longer than you estimate you need. Make a slit length-wise on only one side by ripping it with a table saw, using a thin-kerf blade. Bring it to the boat and cut it to length with a hand saw or portable power saw on-site. Now you will have a removable cover that will snap-on or snap-off and roll with the rode. If needed you can secure a white PVC pipe with white plastic tape. (BTW - the writing on home-center PVC pipe is easily removed with the same solvents you use to thin paints, such as Interlux 202 or 216).