Anyway, like m_c I'm not sure what you're trying to achieve here? Taking 12V dc from the van (battery, alternator?) through the controller into what... some batteries? If so why? Oh are you charging the van battery with solar to offset the power drawn from the engine via the alternator?
I'm converting an extra long wheelbase sprinter van into a camper... I'm now at the point where I'm ready to add two 125ah batteries and wire it all up before i add to much of the interior that it becomes difficult to run wires up and down the length
i'm looking to fit a 250w panel on the roof so i'm not drawing current from the alternator all the time (wasting diesel) and i don't want to be reliant on running it just to charge the batteries, iv also the option of adding a wind gen if the need arises.

sooo... if the shit hits the fan at work and we all get laid off ill park up on the west coast of Scotland put a wind genny up and run my cnc once a week for my beans on toast :)