How to repair cracks in a hard tonneau cover?

My problem is, that after the summer sun, my 3 y.o. hard tonneau developed a network of cracks. They look like being surface cracks only, although at the rear end two splits appeared, each about one eight of an inch deep.

I've asked at the car accessories shop, but they pointed me to an Arallite two-compound resins. Somewhat, don't think glueing would work. Asked also at two body shops, but they didn't know. They actually told me to dump the offending tonneau cover.

So, I'm just curious if anyone has experienced similar problem, and what they have used to correct it. After all, for a hard tonneau cover to last only 3 years, is not good enough.