looking for some advice for installing a new full size trunk pan in my camaro..The trunk pan is too big to get though the trunk opening so whats the best way to install..........Thanks

 

cut out the old pan and weld in the new one from the bottom

 

Be sure to start by holding the new pan up from below prior to cutting anything! Don't want the hole to be too big, and have to patch in. Once you have it underneath you can shoot some self tapping screws through the new pan at each corner to hold it. Then you can go in the trunk and use those screws as a reference to mark the rough cut opening.
After that you can drop the new patch pan and cut out the opening, then screw the pan in again, and use the opening to mark the pan. Once the panis marked you can drop it again and cut the excess material off so the pan fits the opening exactly. Then it's just tacking it in and tack the 4 screw holes closed.