As an alternative (and I hope I'm not derailing this thread), have you (the OP) considered a trailer? While this partially defeats the purpose of a "B", while touring, the trailer can be left behind at home when not boondocking.
Since I boondock at a festival, I plan to have a trailer that I haul there at the start, leave it there for the rehearsals and entire run, then haul it back, so it isn't too bad. Since it isn't with me all the time, it doesn't impact the versatility and compact size of a "B". Depending on the boondocking scenarios, this might be an option for the OP.
With the trailer, this isn't cheap, but one can add a PSW inverter, some panels on top, a battery bank, and a decent charge controller. Of course, placement and weight limits are an issue... but can be solved with some foresight, such as getting a small trailer with two axles and placing the jars between them, so it doesn't affect fore/aft balance.
Another advantage of this setup is that the battery bank is completely independent of the Roadtrek's, because the power goes through the inverter, and 120 volts to the RT is 120 volts. That means you are not limited to 12 volt batteries with the trailer, and can use higher voltages (which means less energy loss due to wire gauge.) Yes, there is power loss due to the inverter, but there would be just as much, if not more, lost if one used long cables at 12-14 volts to connect the trailer to the RT's batteries directly.
Going more exotic (and this isn't cheap), one can add to the trailer solar awnings. These are not cheap... but it is an additional way to add square footage of area with electricity coming in.
Still another advantage is that if the battery bank is large, and there is room for the trailer at the house, the batteries can be plugged into a charger/maintainer when not in use.
For some, a trailer may be too expensive and ponderous, and it might be too much stuff depending on boondocking style... but it is a way to add battery capacity and solar without having to modify the Roadtrek in any way.
On a smaller scale, one could do this, with a collapsible solar frame, panels, and such... and put the batteries and PSW inverter on a hitch mounted cargo rack.
Again, this may be no solution whatsoever, but this is something I'm planning to get around to eventually and built for the boondocking I do.
