Plastic underbelly falling

Has anyone figured out a way to secure the underbelly? Mine is sagging and I see it is starting to rip on one corner.

I assume you mean the chloroplast? That happens, one option I have seen is to get some galvanized steel angle from your local home improvement store. You can then screw that to the frame rales and that give you the support to add additional fasteners in the middle:

Something like this: