Make sure you get a good plug with a valve in it. Blow it up to a pressure higher then the pressure you want to work with and let it sit overnight to make sure you don't have any leaks. The reason for the higher pressure is that the heat of the hot box will take your pressure up quite a bit from the pressure you may have before the unit goes in the box. I have had the plug blow right out of the end of the air hose. Luckily it was right after I put the form in the box and I got it back together without losing the bow.
I don't use the hose method anymore but it worked pretty good for all the bows I did use it for. Things can slide around a lot and they sure do! Good luck in your efforts.