I built a steel 32 ft yacht 36 years ago with a 150 amp arc welder,it overheated badly so I set up a 12 V car battery alongside it with a heater fan,it was a standard Smiths type probably from a Rover 90,it worked a treat.
Or simply buy a 240 v electric fan and with a bit of playing around with cardboard or ply make up an intake for it,even drill a hole or holes in the side.
The old smiths heater fans put out a huge volume of air,I assume modern fans are just as good,flog the one out of your donor!
Maybe a bit of roof drainage pipe throught a hole in the side will do it.David
