The local guy I am dealing with charges $1.08 per watt (tax included) whether 12v or 24v so it all 'depends' how the economics fit. Shipping panels is the killer at any voltage.
I don't know what he will charge for his next batch of panels whenever they arrive from China (later this month?--slow boat etc etc ) OTOH he has so far had a very limited selection of controllers. ( He is mostly a wind turbine guy and grid tie solar guy with a one-man-band home business, so low overhead is the key here)
There is no doubt that RVers are 'low volume' when it comes to solar
