I used 1/8" aluminum sheet for my trigger but steel is easier to find at most hardware stores.
Make something that looks like this. Try to copy the geometry. You want the hinge to be close to inline to the tooth notch in the valve lever. Don't drill the safety pin hole yet!
Mount the trigger and make sure that the valve lever and the trigger tooth match up then drill the hole for the safety pin. You will have to do it at an angle to clear the PC. You may need to turn the ball valve a little so the valve lever and the trigger interlock.
Put in the screw to hold the bottom of the spring and attach the spring.
Mount the tent steak. You may need to drill and put a screw in to keep it from sliding.
Paint it up!
Step 4: Fill Bottle
Make a fill bottle. 8" piece of surgical tubing, a water bottles cap, a small plastic nipple and a small hose clamp. Make this and screw to a filled bottle.
Step 5: Trip Wire Hook
Make the trip wire and wire hook.
you are now done