THe factory used fuel resistant Neoprene tubing. Shrink tubing may be used where extreme flexibility is not an issue. I have seen large diameter bicycle inner tubes used between the motor and boat. It is a cheap solution. The ends can be sealed to keep out moisture. They do not weather well and and deteriorate when exposed to oil and gas. Like rubber water pump impellers, They must be replaced every 4 or 5 years. There are several auto wire loom solutions. One is a plastic that can be wound around groups of wires like a long spring. These are flexible and guard against abrasion but do nothin to seal out dirt and moisture. Likewise a corrugated tube that is split on one side to accept the wires. . . 😉