Originally Posted by NXR
That looks like impact cracking because there seem to be other small ones. Either it was installed and stressed because it was tightened and pulling on the piping or it's flexing a lot when you're standing in the shower or when driving.
Have you looked at whether either was the case? Maybe some spray foam underneath the P-trap could reduce the movement if it's from bouncing down the road.
While I was looking at the lack of engineering and assembly quality of the shower pan support, I realized you could be right. It appeared the lack of structure under the shower pan stressed the ABS fittings and caused it to crack.
I removed the shower walls and shower pan and discovered a big chunk of the shower pan support was cut out and missing. No wonder why my shower pan felt "squishy". It appears the Forest River "plumbing technician" cut out the support so the pan could be dropped in with the P-trap in place. No need to try to connect plumbing through a 5"x8" hole, right?
I cut a 22" by 36" sheet of plywood and screwed proper length 2X4 supports under it. Now the shower pan is supported with no soft areas.
I have so much fun fixing Forest River quality.