my apologies i may have misunderstood your thoughts/questions.
i,m not the person to answer why 1.6 steel was chosen for the design ( maybe Chris will confirm the reason ).
i,ll be totally honest & say i had the same thoughts as you whereas i had the offer of free use of an arc welder ( my brothers ) before i started my build & asked the very same question... can i use an arc instead of a mig, i decided once i,d done more research into the building of the chassis that mig was the way to go,
i bought my mig off the "mig welding forum" second hand for £50, its a 150amp & came with 2 large pub style gas bottles so the bargains do come up now & again, guess i was lucky as it works perfectly.
i,m trying to build to a strict budget, ask Ash G
& as close to the book instructions that my ability will allow.
i think if you used the heavier gauge steel it may cause more probs than it alleviates at first.
best wishes for your build by the way.
cheers
andy