Tracy,
Welcome to the weird n wonderful world of
U-Haul campers.
At the top of the page, in the "More" drop-down, is the "Document Center"... and toward the end of that page, under "Manufacturers", there's a guide you can download for a full rebuild of the
U-Haul windows.
Fiberglass RV - Document Center - U-Haul Side Window Repair Information
A number of folks have used that guide to rebuild their
windows. They're still a little fussy, even after that, but at least then all the materials are new, and the chances for eliminating any persistent
leaks are good.
Some folks have just gotten windows custom made---Motion Windows is one source. [but several hundred dollars per window]
Some have made fillers for the opening, and installed the smaller
Scamp windows.
I slightly enlarged the openings on our CT13, and put 20x24 horse-trailer sliders in the side windows [very affordable, but there's that having-to-modify the opening thing], and a
Scamp rear window.
Best of luck, whatever way forward you choose...
Gary