I would move it back a foot.

Can you put a rack at the fwd end of the cab? That's what I did and it works great. My truck is about 18' long and the spacing of the racks is just over 7' apart.

When I have the 21' triple on it, the front end of the kayak is even with the front of the truck with 3' hanging off the back. I tie the front end to the front bumper because it extends out there a ways.

When I put my 18' single on it I don't have to attach end straps because the racks are so far apart on it and the front end doesn't extend as far fwd. I've cruised down the freeway with no problems.

I've had no problems from the flexing/twisting of the truck if that's keeping you from doing it that way.

Another thing I've learned the hard way. I put black pipe insulation foam on the racks I built. The problem is that once it gets hot out the foam stuck to the bottom of my kayak which I had to remove with a scotchbrite pad. I now use closed cell foam on the rack I built for my sons kayak and had no problems.

Go here http://f1.pg.photos.yahoo.com/fastmountainbiker click on the kayak folder, and then check out the yaks_on_truck_small picture.