If you are talking about the plastic boxes for the 110 receptacles you should find 2 small plastic wings that fold out of the side of the box as you tighten the screws at the top and bottom. Make sure the screws are far enough back out that they will allow the wings to swing out and clear the back side of the wall as you tighten the screws. Once the wings go out they will hold the box in place.
If this is not what you are asking about yes a picture would help.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles