I recently bought a 1992 Camaro RS and discovered that the left trailing arm mount was rusted off the body after driving it home after the deal. Currently the only thing holding the trailing arm off the ground is a shoe string. I haven't driven the car since I found out about it but I am wanting to know what the best way to fix it would be.

 

The best way to fix that is to buy another car.

There seems to be a rash of this kind of thing lately "How do I fix my mortally rusted Camaro" threads. The fix is straight forward, you have to cut away everything with any rust that doesn't scrub off with a wire brush or sand blaster, and weld in new metal. As bad as that looks, you'll probably be cutting away a lot of the car to get back to metal you can weld without just burning through. When you consider that there aren't many reproduction metal parts made for these cars, you're usually going to be looking at making the repair panels yourself, or getting them from a donor car.

It'd probably be easiest to just find a nicer car to begin with.