I've always used teflon tape and had good luck - several years running on the same plug. It can be used for gas or water, but not gasoline, oils, etc. My cousin is a plumber and he recommended I use the tape, since I remove it frequently. I carry a roll of the tape in my toolbox, in the truck bed. It has come in handy for other things, as well.
The plastic plug should last quite awhile as long as it is not overtightened. But a spare is always a good idea.
2015 Jay Flight 32RLDS Elite
2012 Chevy 2500HD Crew Cab LTZ (6.6L Duramax/Allison)
Equalizer Hitch (1200# bars)