Take a look at this FullTimer's site and the rack on his truck:
Here's what he posted:
Mine was made by Brown Mfg. of New Braunfels, TX.
I had them installed at the plant. They are called Weekenders,
and are removable when you are not hauling the boat. I'm sure
other people make them. Back in 2003 they were about 80 bucks
Here's an example I just found by somebody else, and quite a bit
Mine are not adjustable in width. They consist of a couple of
upside down "h"s made of one inch steel tubing, braced for
strength at the arm, and they slip into slots permanently
attached to the truck. In the front I had the receiver welded to
the inside of an upright to my brush guard. In the bed, right
behind the cab, there is a slot inside the bed rail and another
at the bottom, on the bed. It's important to have two brace
points, or you can torque your bed rail.
I have an extra receiver at the rear of the bed, so I can carry
the kayak over the bed when not hauling the trailer. In fact I
had a rack system built for each side, in case I want to carry
two boats. I never have used both, though. I just carry the
spare around in case I find a great deal on a kevlar canoe.
My particular rack was something of a custom job in detail. In
addition to the "h"s, because the length of the boat was only
slightly longer than the distance between "h" supports, I had
them make two long rails to support the boat between the "h"s.
When these are bolted between the "h"s, the whole thing becomes
stronger and more rigid, and the frame of the boat doesn't have
to support itself. It also makes it easier to mount the boat for
one person. I just stick one end on the frame in front, grab the
other end, and push the boat up and slide it back. With only the
"h" end supports, I'd have to manhandle it more, one end at a
time. If you have a regular cab, or a longer kayak, you may not
need the middle rails. I had them built in two sections about 6
feet long that bolt together, so the whole system could break
down and store in the back of the truck.
I have seen a similar canoe rack where the rear "h" swivels. You
load one end at 90 degree angle to the truck, and then swing the
other end around. I find it more convenient most of the time to
just load it from the front. At a boat ramp it doesn't matter
much, but when you are nosed in to a bank between trees and brush
you can't do much swiveling.
I have also seen regular headache racks right behind the cab used
in combination with a T in front that slips into a centered
receiver hitch. Personally I like carrying the kayak off set to
the right. I hardly even notice it's there when driving, as the
rear view mirror hides it. In the center, you might have trouble
seeing traffic lights
and such. In any case it would block your