The only trick is to tie down both ends of the frame twice. You have to tie it down high and low. Low only and the bike will fall over. High only and the wheels will walk out from under and it will fall over.
Oh, and tie it down so that it stands upright.

Of course I know about this stuff, do you know how many Harleys I've owned?

Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python