That fresh water tank photo I posted has no steps or ledges. It is shown in the upright position as it goes under the B. I haven't examined the grey and black tanks but I doubt they would have steps or ledges either.
But getting back to tank capacities, there is more than just size and figuring out how to maximize. The other factors are the space available no matter how you maximize the size and the overall load capacity of your B. Those last two factors are why Travatos, Agiles and Ascents have smaller tank capacities.
