I would suggest taking a look at one or more of the commercially-made models of helium balloons for this purpose - start with
www.parabounce.com.
Also, if you are seriously delving into this project, visit
http://www.balloondispatch.com/repair.htm to get information on balloon repair stations in your area. They will be able to help you out in your quest for information, or at the very least, pass you on to someone who definitely does.
Another person to contact would be Don Piccard of Minneapolis, MN..
long time now and has a vast wealth of ballooning knowledge which you should tap into. Tell him 'Rat' sent ya!
Good Luck, Jon Radowski