Dealer quoted $700 to run wire for backup cam, Need Advise

Not sure what type of rear trim you have on the corners but if it's the type that has the plastic insert you can run the wire inside that insert. Did it on our current 5th wheel. You just need to re-caulk the trim at the top and bottom. I ran a wire from inside the 5th wheel, then under the frame and up the rear corner for an XM sat antennae.