If the bulb is capable of tripping your shutter with 20' of thin rubber tubing, you may find that you can go to 30' that by replacing the rubber tube with 1/8" vinyl tube. It won't be as soft and easy to roll up, but it'll be a lot more positive.
1/8" I.D by 1/4" O.D, A bit stiff and bulky, but commonly available at local hardware stores:
Slightly more flexible (3/16" O.D.)
For super flexible, absolutely guaranteed not to "balloon" like rubber tube, use Polyurethane tubing.
The 1/16" I.D. will assuredly give you double the useable length of your bulb. It might be a bit sluggish to fill the cylinder, but it WILL guarantee full pressure to trip the shutter. And it will probably coil up just as small as the rubber tubing...