Wiring dual battery solar charge controller from trailer to van

[pepo1]

I've got this EPEVER Duo Racer 30A charge controller situated in my trailer as part of a solar setup for charging an auxiliary battery in the trailer. I'm gonna use it to charge tool batteries, run some lights and other small bits and pieces. The charge controller is designed to simultaneously charge the tow vehicle starter battery as well as this auxiliary battery. Can I connect the charge controller to the tow vehicle's starter battery through the existing trailer connector (the connector that runs trailer lights and indicators), rather than run dedicated wires back to the tow vehicle battery? If so, how? The trailer connects to the tow vehicle using 7-pin flat connectors as shown in the attachment.

If the trailer connector won't do, do I just run a positive wire from the charge controller to the starter battery positive terminal? And where's the best place to attach the negative wire from the charge controller?