Is it leaking from inside the wcv or is it leaking from the fitting?
At any rate if it is leaking from the fitting unscrew it, get some Teflon tape and seal it up.
If it is leaking from the inside take the top off (be careful of the spring flying off) and you should see a rubber diaphram held in place with a metal clamp. That metal lamp has most likely worn a hole in the diaphram. Go to the hardware store and get a zip tie and some silicone caulk. Replace the metal clamp with the zip tie and dab a little caulk on the hole the metal clamp wore into diaphram. Let it dry proper and reassemble. You should be good to go and finish your camping trip.