If you guys are having that much trouble you're using the wrong materials. You should use only REAL Tygon. The fuel lines that come with most ARF's are yellow vinyl. Additionally a lot of places that sell yellow vinyl call it Tygon, but it's not.
Real Tygon is a cloudy yellow and has F-4040 printed on it. The stuff Dubro sells is real Tygon. Yellow vinyl will last for 2-3 years whereas real Tygon should last at least 5-6 years. Additionally I use Viton tubing inside the fuel tanks. Viton will last indefinitely in a fuel environment. It's what is used inside automotive fuel tanks to last the life of the vehicle.
It's not good practice to use tie-wraps to secure fuel lines. They pinch the tubing providing a potential leak. Use safety wire and wrap it around the tubing twice.
I recently re-plumbed two of my jets that are 8 years old. The Tygon was still flexible and worked fine, but I figured it was about time. Also I do not store my planes with fuel in the tanks.