Being retired, cheap and not very electronically adept. I found the middle of my camper and took a red paint marker and a straight edge and put a vertical line on the camper from the bottom to the curve where the bunk transitions to the body.
My sliding window splits in the middle so I open both sides about 1/2" and back in with the paint line centered in the opening. Works every time. I use the truck review mirror and thats it. Very seldom do I use the west coast side mittors to back in.
I like the laser method but my painted vertical line works too.
