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If you don't mind taking the time. How about taking a length of 7/8ths pvc pipe, cut an 1/8 inch slot its length, put tape over the slot, either wax or pva the pipe, then fiberglass the pipe with several layers. Sort of roll the glass around the pipe to your desired thickness. When set up, twist the pvc pipe out of the fiberglass tube as it will give being slotted. Boom your own fiberglass replacement tubes. Glass those into place. Just a thought.