With that set up I'd worry about the bikes hitting the rig when making tight turns... There's a set up we've seen that attaches to the tongue and carries the bikes up above the propane tanks...it was pretty slick...I'll try to find a post that describes/shows it and post back...
WOW! I surprised myself...I found it on the first try:
http://www.airforums.com/forums/f161...ams-41078.html WE saw this rig at the Balloon Fiesta rally two years ago...I'm sure the poster will be happy to give you more info...
(Just don't put them on the rear of your trailer...there's lots of discussion on the Forums of why that's a bad idea...)