A small portable 115/230 volt dual voltage welder such as the Miller Maxstar 150 S will work with 5 kw generators,while you can still get fuel. It’s not cheep, but If you can afford it, I think it’s a good choice. Cheaper welders are available but I worry about the reliability. Use 3/32″ 6011 and 6013 welding rods when buying rods. 1/8″ rods are also an option but they require more amps. Buy them in small packages of 5 pounds, Moisture attacks rods when they are opened, so small quantities are best. I have used this setup for remote welding and have had good results. Buy several packages of rods because when SHTF you will have a hard time getting them. Welding skills when SHTF will be valuable if you have the equipment.