I have found that cheap vent covers still become brittle even when under a Maxx air cover that is untouched by the Sun effects. This happened on my T310SR.
I do not know if the cheap actually a defect or not. I happen to be a lucky one to get 2 batches of bad vents covers. During the 2004 year models Sunline changed vents suppliers. On my T2499, they started rusting within 1 year. Sunline was still in business then and they promptly sent me 3 new ones and I replaced them. However on the 2004 T310SR, well Sunline was not longer and I had to replace them. I went with Ventline. That trailer had Maxx Airís on it must have been since new. Yet the vent cover under it was crumbled into almost a 1,000 tiny pieces.
The Maxx air covers are worth the money. They plastics they use holds up to the Sun. I do put 303 UV protectant on the inside and outside of the Maxx Air and the new vent covers I installed.
Since I bought mine, I found Camco makes a vent cover replacement with a lifetime guarantee. If I would of known of that, I would of went with them. http://www.camco.net/Menu.cfm?SupCat...ProductId=2193
The lifetime ones are listed as made out of polycarbonate. The also make a polypropylene but it does not have the lifetime warranty.
Polycarbonate is what Nalgen water bottles use to be made from or Lexan. Use to meaning they responded to the Bisphenol-A (BPA) situation where any food producers are now almost immediatly converting out of that plastic. However Polycarbonate is good stuff, just do not eat off of itÖ. Polycarbonate sheets are used for guarding in Industrial applications as it will not crack and when thick enough is very close to indestructible under semi normal conditions. If I remember right I though it would stop a 22 bullet.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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