Truck Forums - 3500 dully plastic fender crack in cold temprature

I have a 2004 3500hd dully, I live in a COLD climate and I am on my 2nd set of rear fenders or quarter panels.

We have had temperatures in the ZEROS over the last month and a few cracks have appeared in the lower section of the rear panels. Not sure how the cracks happen, in one area of the panel, I backed into a snow pile and the fender just shattered. I have the pieces. I am not alone in this, all the 3500 in my town have busted, crack missing sections of rear fenders. I just want to fix the cracks and put the pieces back

I have drilled each end of the cracks and the cracks have stopped running.

When I disposed of the first set of fenders, I kept a piece of the fender to test repair techniques. Yesterday I found the test piece of fender in the garage which is about 60 degrees, and I tried to bust the piece so that I could fiberglass it back together. I could not break the piece, it just bent. I set the test piece outside for a few hours, the temp was 20 degrees and I had no problem snapping a section off.

So I sanded the back sides of both section, taped the section together on the front, with a 1/16" gap and fiberglassed the pieces together with 2 layers of cloth... Today, I gave the repair a test and I was able to separate the repair into to 2 pieces without much effort, the failure occurred at the fiberglass plastic bond.

So there is my story. Fiberglass is not the repair solution.
How do I fix the fenders?
What is the plastic compound that the fenders are made from?
The wife said that a flatbed is NOT an option...

Thanks