With a fork brace and the big pin in that the RMATV one comes with, I've not had a single problem with using only two straps. If you don't use a fork brace and you don't have the pin, then I wouldn't use one. You'll blow your seals out if you try to take up enough of the suspension without the brace and if you don't take up enough suspension then you'll surely drop a strap and then there goes your bike....
What is this pin you speak of? I can't even find the hauler at RMATV.
Doesn't everyone use a fork brace? I thought that was the first thing you buy after you get a bike.