Last year at elevation they let us use thread lock on our robot and they still passed us for inspection. This happened at our local comp and at the world championship. it was listed in the bill of materials as well. Because they let us do that we were wondering is we could use a spring to open and close our bucket for our balls. Does vex have any official approved springs somewhere or can we buy our own and use them like we did with the thread lock. 
Chuck gave a most excellent response. We use the VEX latex tubing anywhere we wanted to use a spring.
Ah the age old bucket design. Instead of spring design, try working with a winch system. With spring/rubber, the door will “bounce” but it won’t bounce all the way back up…try the winch. 
is there a limit on how much latex tubing you can use?
Nope. Use all you want. 