I have been doing that and some things just do not tie down very well that way. I found tie down straps at expediton exchange that look like they will help.
Thanks for the link and information Volhoo, will get one of those barrier nets soon. Used bungee nets before and the tangling can get exasperating.I'm pretty sure this is the online vendor I bought my net from.
Cascade Nets :: Barrier Netting
Mine is 4' x 8' which you won't find on their list.
Give them a call and they will make any size you want (they are all hand made of course).
Mine is the #21 (second one down on the page), 209 LB Single Strand Tensile Strength, 836 LB Mesh Bursting Strength.
I think it cost around 50 bucks (that was a few years back).
I use some of these for roof rack loads, as well as for their original purpose, loading motorcycles. Very versatile item..I run the strap around the bar and hook the strap to itself when it doesn't fit on or around whatever I am strapping to.