It must vary by RV brand and model. Our Komfort (no longer made) came with #8 wire for the solar pre-wire. One pair from roof (actually was dangling in the fridge vent ready to be hauled up to the roof) to the kitchen where it was taped to another pair going from the kitchen to the battery area up front, dangling there.
The idea was to put the panel(s) on the roof and attach the pair out of the fridge vent, insert the controller in the kitchen area between the roof pair for input and the battery pair for output, attach lugs to the battery end wires and connect to battery.
This left the controller miles from the battery, so the other way is to join the two pairs where they meet in the kitchen so it is one long pair from roof to battery area, put the controller there with that long pair as input, use short wire you supply from controller output to battery with a fuse you supply on the pos wire near the battery.
