"Duracast standard tank wall thickness is barely 1/4"...50% thinner than Ronco. You can order tanks with 3/8" walls from Duracast, but only for a huge upcharge in price."
The question is always "proper installation."
If the tank is supported outside as most mfg prefer , esp for an offshore boat , thick or thin , no difference.
If the tank is thick enough to stand alone , with no box or foam to stabilize it , just hold downs , that would be worth extra cost and shipping expense.