and here's a thread that gives lots of reasons for never transporting a tank on its side http://www.rvnetwork.com/index.php?showtopic=104109
That would be my alternate method, as I've done that before just strapped it to the rack on top. But sounds like that's an even worse idea...
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 07 TTR90, 07 CRF50