Floorpan Modifications

I'd like guidance on modifying the floorpan in my 2009 Chevy Impala. I don't know what to do to identify what is safe to modify and what is not. That's what I'll use to begin deciding what the best approach is to flattening my floor to use it for storage.

Flattening the floor? In what area? If there is any thought of removing the center ridge/hump you might as well forget about it. That formed area gives the unibody much of its strength.

Of course, it you want to design, fabricate, and install a true frame like Impalas used to have, you can do anything you want with the floor.

I've decided to instead use the bolt holes opened up by removing the passenger front seat and rear bench seat; I'll bolt down boards as I cut them to fit which will make for a decent flat and level area. I can always put doors in for "stowaway" spots... Ideas ideas.