I think steel is an excellent idea, so is a stick welder, but I would still like to take this opportunity to screw up your whole design at the last moment because that is what I do best
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When a weld cools it solidifies then shrinks. The shrinking bends everything out of shape with no possibility of correcting it. If you are a novice welder your welds are unlikely to be drop dead gorgeous and the effect is amplified.
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Meaning you end up with a framework that is wildly out of square, it fills half the workshop, is tricky to get it out the door and take it up the dump.
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If you are fiendishly clever you can try to pull everything square by welding in cross braces after the event and hold the thing in tension.
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If however you plan ahead and weld plates bearing bolt holes to your bars you have a chance to straighten things up after everything has cooled down. A round file can move a bolt hole, an angle grinder can square up a face, packing can be tack welded in place.