I have a large 4"-opening Packard shutter that works great, and I'm going to purchase a really long rubber tubing for it. But high quality silicone rubber tube is not very cheap, and besides I have to buy oversears and pay for the shipment too as I was unable to find a black one locally. And therefore I guess I'd better not buy any more then I could actually use. So, my question is, how long a tube is still OK to reliably open and close a Packard that size? What about a 100 feet? 200 feet? even more...? Any practical experience is welcome. (I don't want to switch to an electrical release type shutter.) Thanks!