Get onto song of the paddle:
http://www.songofthepaddle.co.uk/forum/showthread.php?23826-Cars-and-Canoes-a-visual-guide
To be brutally honest; it's a doddle,far less terrifying than many would have you believe heres a few of my efforts;
The first time I carried a canoe-it
really was unpleasant
No foam on the bars and 25mm straps-bad choice! You want 2 x35mm x 4m (minimum-better with 5m length) cam straps for securing the boat to the bars and 2 x 25mm x 4m-5m cam straps; one for the front and one for the back. Then fit some proper foam pipe insulation, not the cheap stuff from B&Q.
(The canoe was crxp as well as it turned out- Old Town Discovery 158 = pants!
)
Then I got rid of the Old Town Discovery 158 "Bath Tub" and bought the best polythene boat I've had so far,( actually; almost certainly the best poly boat you can buy)the Nova Craft SP3 Prospector, Oh and I changed my car again too
In this picture, I've rigged a pair of bonnet loops, as well as the tail strap but I did away with the bonnet loops and went back to using the front tow loop-much more secure in my opinion.
With my new Fiesta, I couldn't reach the rear tow loop easily and the strap would have been in contact with too much of the bumper, so I made a "y" strap for the hatch instead:
Rigged like this, the boat simply does not move when properly fastened.
You shouldn't really have any issues with a 4x4, the bars are usually so far apart that you get very little fore and aft leverage or "rocky horse" movement, though we always use the nose and tail straps regardless.
If you have roof rails fitted, as below;
you
can get away without the front and rear straps but
I'd recommend using them regardless
hope this helps
Cheers