I have about a 10ft section of 300Ohm twin-lead laying on my concrete roof tiles, from a vent to the center of my dipole. Do I need to insulate the twin-lead from the concrete roof?
Well, I own a tile roof cleaning company here in the Tampa area www.saferoofcleaning.com
and see moisture up there quite a lot.
The tiles on a roof can and do get wet, and retain water, from both the rain and humidity here in Florida.
I think the water might effect the twin lead, but you will have to measure to be sure.