Then I bent the 30 x 5 mm mild steel using a torch to heat up the area to be bent to red heat. This makes it very easy to bend by hand. (Red hot steel has the consistency of lead.) Also, the oxy-acetylene flame is very narrow so the heat is concentrated in a narrow band and the bend is quite sharp.
You could also bend the steel cold in a suitable (large) vice but it would need some hammering to get a sharp bend.
Hot steel can just be bent by hand (and un-bent if it doesn’t quite fit the pattern.
The excess can be easily trimmed with a 4 ½” disc cutter or a hacksaw. (The disc should have a guard but it’s a lot easier without. However goggles and gloves are essential. The disc is very light and therefore stores very little energy, so a shattering disc will only cause moderate injuries - but you have been warned!)
A bit of a bevel needs to be filed before welding and it helps to clean off the black mill scale from the vicinity of the join. An 80 grit flap-disc on the 4 ½” grinder is best for this.
A not quite perfect but good enough MIG weld. I weld both sides and didn’t bother about any grinding down or cleaning up - it will be 10 feet up and (hopefully) covered in vegetation!
Centre-punch in the centre of each side and drill 5.5mm holes for the 5mm screws which will hold the whole shooting match together.