not another solar question ??

Bobbo wrote:
The closer the charge controller is to the batteries, the more efficient it is. Distance from the PV (solar panel) is less critical.

true for MPPT controllers, somewhat true for PWM controllers.

With a PWM controller if the battery is deeply discharged it lets full panel current to the battery and voltage is regulated by the battery and internal resistance. Where the controller is really doesn't have much if any effect on charge current. As the battery nears full charge it switches to a duty cycle square wave, and here is where distance matters since now voltage drop between the controller output and battery will limit charge current and increase charge time needed for a full charge.

For a MPPT controller it sets the voltage at the output of the controller during the entire charge so voltage drop in the line working against battery voltage and internal resistance= low charge rate. And since MPPT controller output current is higher than input current during initial charge, voltage drop between the controller and battery can be more limiting than between the panel and controller. Especially true if the input to the controller is a series string of panels. So for a MPPT controller it is important to have the controller as close as possible to the batteries.

The closer the charge controller is to the batteries, the more efficient it is. Distance from the PV (solar panel) is less critical.

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I'd put the controller in the truck, that way you only need one instead of in each trailer. I'd connect the output of the controller to the charge line going to the 7 pin on the truck. If you're not towing a trailer it will keep your truck battery charged up. If you are towing a trailer it will keep your trailer battery charged up.
To make this work your charge line has to be hot all the time like on a GM truck, not switched off with the ignition like on a Ford. SOME charge controllers can be damaged if the panels are hooked up with no batteries.
Also, you will need to have very similar batteries in all your trailers and truck or you will have to be changing the absorb and float settings on the controller for each trailer. If they are all flooded or all AGM of similar brand it should work fine.

controller should be as close to the batteries as possible, especially if it is a MPPT controller.

Mount it such that the controller stays connected to the batteries when the panels are disconnected, otherwise the controller can be damaged. Or have a means of disconnecting the panels first and reconnecting the batteries first.