I have two favorite products for sealing pipe joints
1) Pink teflon tape. This stuff is thick. Thicker than yellow, which is thicker than white. Only place I can reliably find it is at Lowes.
2) hercules blue block. sets up tough but flexible.
http://www.herchem.com/specs/block.pdf. Not NSF rated for drinking water.
The theory behind not using tape with gases, is that if a piece of the tape comes off it can get stuck in a valve and prevent proper metering or even shut-off of the gas. If you wrap the tape 2 threads up, and make sure you clean out joints when you un-thread them, you're probably safe. I just stick to blue block for gas lines.
PS: Blue Block will clean up off your hands and tools with isopropyl alcohol. but clothing will be permanently stained.