This is how I make the best trolling handlines on earth. I see no reason for gatekeeping the manufacturing method, so if this helps someone, I'm happy.

They are available on my website in 50 ft and 100 ft models.
50ft has 1 foot of rubber that stretches to 3 ft for 100 lbs of resistance.
100ft has 3 ft of rubber that stretches to 9 ft for 100+ lbs of resistance.

www.lancelures.com

The rubber is a customordered Primeline Bluwater formulation with 1/4 in inner diameter and 1 in outer diameter. Your typical speargun band (5/8 in OD, 1/8 in ID), will provide about 1/31/2 of the resistance of this stuff, and the inner diameter will not accommodate the Amsteel Blue.

Be safe and remember to wear gloves!