I would use the 1/4 inch it is going to be stronger than the thinner ones and not going to weigh much more but you might want to look at 2 by 3 tubing insted I think that is what they use for the samurais
What are the reasons behind using 2"Wx3"H? Is it strength issues? I was thinking of using 3x3 so I wouldn't have to grind down the end caps(original mounting to body) to fit in a 2" wide space. Thanks again in advance.