I also have attached garage. I have welded in there, but minimal and with the door open. I keep my car outside. it was tarped for a couple years..so I didn't have to bale it out between working on it. Will be again soon when I work on the doors. I did the formed pans up front and a couple small pieces in back. that one looks pretty easy. I would just lay it on and stitch around. Use weld thru primer between and (I didn't know about that when I did my floors, but used it on most of my body repairs) Just seal it really well from underneath if you overlap. That's where I used the Black Jack Neoprene roof caulk.
