On the trampoline thing, I switched from "line" to rubber bungie cord (10 feet of 3/8" I think?) on my Hobie 18 and I LOVED the tramp after that. Now, it will bounce you from tack to tack, which is fun, but it will always be tight with no sagging.

The cat catalogs sell bungie tramp lacing kits but I just went to the hardware store and bought a bunch of it off the spool for less than half the price of the kits. No, it won't last for 10 years out in the sun, but it's pretty cheap and easy to replace after a couple years wear.