I am going to stick with steel rod ER70S-2
Wanted to share my thoughts on the floor as there was not a lot about it, anyway having fun today with the GT 40 I got a sheet of 16 gauge steel for the floor and cut it into 5 squares 2 for driver, passenger 2 for rear motor area 1 for front suspension area. Each section (.057 thick) was welded to frame (.125 wall) since I am just trying Tig welding out. I would like to share these thoughts. Gas flow 15 CFH Amp 110 cup size #6 Radnor 1/16 electrode ground to 30 degree tip. I used an aluminium block to keep thin metal cooler and to hold it down. Otherwise it will warp real bad.
They welds look like they penetrated good and the pool of melted metal was clean with no bubbles or splatter, and the welds were nice shiny color.
The thickness at 16 gauge was nice and stiff and not heavy. I also did each weld about and inch with a 1/4 gap between each weld for crack out if that were to happen. I think I will send out a sample section to NDT testing for mag, just for fun to see if the welds are correct. Thanks for all your thoughts and suggestions.