Have you looked at either an auto parts store or a store that sells replacement parts for trailers (here in the Midwest, Northern Tools and Electric is such a place. Maybe you have something like it in Oregon)? A farm supply store might have something too, assuming your taillight lenses are standard parts. I don't know your unit so I don't know what the lenses would be like. Is there a Rockwood dealer nearby? Maybe they could get replacements. And there's always RV supply houses on the web to check. Failing that, a good glue....?
Later: etrailer.com might have something like it, though you might have to phone them (800-298-8924) rather than search their site. They might not carry your lens but may know of a supplier.
It's never too late to have a happy childhood!
Lee, WU0V, and Courtenay, N0ZDT
2011 Rockwood A128
2000 Silverado 1500 pickup
60W solar system
2000W inverter generator