My solar controller is mounted on the wall in the pass-through storage compartment near the batteries. I have a 150 watt solar panel on the roof and a 100 watt portable panel that I move around on the ground. I connect the portable panel to the controller with two cables that have 2-Pin SAE quick disconnect plugs.
The first cable is around five feet long. It is always connected to the controller and runs through a hole in the floor of the pass-through storage. Yes, drilling a hole is necessary, but it is a small hole drilled through the plywood of the floor. Sealant was used in the hole where the cable exits the floor. The cable to the battery could be run through the same hole. The short cable under the trailer is attached with Velcro to the metal propane line that runs under the trailer. This keeps the short cable neat and tidy and out of the way. The cable is easy to reach, being just a few inches under the trailer near the pass-through storage door.
The second cable runs from the portable panel and plugs into the first cable with a 2-Pin SAE quick disconnect plug. It is quick and easy to connect the portable panel to the controller. This configuration works great to provide extra charging power from the portable panel.