Are you welding from inside the car?
If you are doing it from underneath, you could just slide a piece of sheet metal between the Metal floor and the Rug.


Nothing wrong with safety but you sound wayyy safe with the gas tank. Unless you can really smell fumes, you are not going to have an issue. Watch the guys at Muffler shops go to town with their cutting torches.

Don't run a complete bead the length of the piece. Stitch it in at 1/4" welds or it may get too hot and burn through or warp the area. Slight circular motion..Start on the Original floor and circle up and touch the edge of the new piece then back to the original floor. You will find the new piece will not fit super flat to the original floor. tack the spot that is flush to the floor then tap another section down and tack that. work your way around the piece. then go back and hit it with 1/4" runs.

Keep a spray bottle of water handy. Some old paint chips or undercoating or.. whatever may catch fire.. no biggy, just a little spritz or a pat with a gloved hand will do the trick.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/