what type of line to use to run propane

[Sevo]

After a quick internet search her is one link: http://gashosesandregulators.com/lowpressurehoses.html come to think of it mine may have also been 6 footers not sure, being it has been awhile

you are a google master! I couldn't find the things to save my life, I have been searching all morning!. Thank you so much for the link and the help

I am assuming I would want to buy the 5 PSI max hose?

[Shadow Catcher]

I just went through this exercise and dumped the 1/2 black iron and installed 3/copper from tongue to three way branch under the trailer and up to the gas point, cook top and water heater. The only hose is from regulator to POL fitting at the tongue.
Copper is acceptable under RVIA standards.

[Sevo]

I just went through this exercise and dumped the 1/2 black iron and installed 3/copper from tongue to three way branch under the trailer and up to the gas point, cook top and water heater. The only hose is from regulator to POL fitting at the tongue.
Copper is acceptable under RVIA standards.

Is 3 the size of the copper you used? What is the best size copper tubing to use in these?