GMC 2003 Sonoma Owner's Manual page 124

Notice: Loading cargo that weighs more than 100
Ibs. (45 kg) on the luggage carrier may damage your
vehicle. When you carry large things, never let
them hang over the rear or the sides of your vehicle.
Load your cargo so that it rests on the slats and
does not scratch or damage the vehicle. Put
the cargo against the side rails and fasten it
securely to the luggage carrier. Put the main weight
as far forward as you can.
Don't exceed the maximum vehicle capacity when
loading your vehicle. For more information on vehicle
capacity and loading see Loading Your Vehicle on
page 4-49.
To prevent damage or
loss
of cargo as you're driving,
check now and then to make sure the luggage
carrier and cargo are still securely fastened.
Bed Rails
If your vehicle has bed rails, they are there for
appearance only. If you try to tie down a load
with them, or to secure things in your truck,
not only can it damage the bed rails, but the
load can loosen. This could cause injury to
you or others. Secure loads by using the cargo
tie-down loops, inside the truck bed area.
2-49