floorboard patch welder?

Hello everyone i am in the process of doing a roll in bedliner and while sand blasting some rust out i found alot of holes under and around the roll bar mounts behind the front seats. I have also found that the seat mounts are cracked all around the holes and have managed to break one of the seat bolts trying to get it out. Im thinking of cutting the chanel under the tub that the seat bolts through and welding in a piece of. 1/4 inch plate to bolt the seats to. What i want to know is if my welder will handle it. Its a millermatic 140 autoset and i got 35 flux core for the job. Also would yall go on top or bottom of the tub? I do have a copper welding spoon and have done some body panels in the past but that was with oxy acet. Thanks for the help.



Also i cant aford to get gas atm so thats a no go there the local shops want way to much for it.