My 1971 trailer is as strong as it ever was...The fibers are glass anyway...They are timeless, the plastics used in older ones are different over today's epoxies, Back when the dinosaurs walked they had nothing added to them to handle UVA or UVB breakdown of plastic materials, so gel coats in the arid regions can be dusty or in need of attention...I re-did mine with additives one can buy now...I never met a fiberglass trailer I did not like someway...There are issues unique to them true...All in all I have owned them for 25 years...My buds are not so lucky...I will keep fiberglass...Ask Airstreamers about rivets...
On the axles...The torsion axles have rubber in them often, these age like tires
, aging at a set rate because the materials outgas steadily and breakdown getting more brittle like clockwork. Its because of the chemicals they are made of and the vulcanization process of synthetic rubbers. In the era of the 70s the rubbers used were completely different chemical chains...These deteriorated at reliable predictable rates...They are also inexpensive for their duty cycles the new ones are better now.
Predictable is good...No surprises, you know when to watch and when to replace.
A point I would like to make today is a simple one, these axles are on everything pretty much...Mine are leaf (steel) but the plastic bushings used in them needed to be replaced and of coarse it was a pain...but ah the fun I had in 20 years...From that point of view its cheap.
Fatigue fractures do occur in metals as well, I have had to address this from time to time in my trailers and in all trailers I have ever owned...In the old days arc welding was the standard welding technologies in practice, now its wire fed exotic gas envelope welding which produces a cleaner better weld...So much so some frames are becoming thinner and lighter as a consequence...I prefer the older heavier frames so I inspect my trailer at the beginning of the season as a good habit and would anyway.
My 95 16' Scamp
had the same issues with the frame as did the 1971 Astro...I do not see any any disadvantages in the age of fiberglass trailers over younger ones or have I seen any in the various clubs in Arizona.
The cost of these trailers are mainly labor and insurances in their manufacture anyway...Not increases due to superior materials old gen vs new gen...A well maintained unit is a bargain and the money saved money best spent making memories in our trailers.
Go for it...Be a little picky,Talk to others, You will end up with one I think.