In a former life I used to fabricate and install Corian counters. While it rarely happens in stick-built homes, Corian or other synthetics can crack but it's usually caused by improper installation. I have noticed also that some synthetic countertops in RVs are not as thick as what I used to fabricate.
When installed in an RV, it should be affixed to the cabinets with a very flexible silicon-type caulk that is not compressed too much so that normal road vibrations are dampened. So, it's very possible that the RV mfgr. didn't install your counter properly and it cracked because of vibration, especially during colder temps. I would not recommend trying to repair the crack as I believe it will re-open in time. Hopefully, you can obtain a replacement from the mfgr. without too much hassle.
--2005 F350 Superduty Crewcab, 6.0, 4wd, short bed, 3.73 gears
--2016 Montana 3711FL, 40'
--SOLD 2014 Wildcat 327CK, 38'