This is beyond easy, but I did see people asking the guy who built the first one how he did it so I documented the process. Yes, I know you just drop them in a pvc canister put a valve stem and glue. Here's the process I did.
1. Purchase 1x valve stem with the rubber grommets from your local auto store. You also need to stop by the hardware store and pic up 1 12" section (i cut mine down to about 9") of 3" pvc pipe. Also, purchase 2x 3" end caps for that pipe. While there, pick up some pvc cement.
2. Cut the tube to your desired size and glue one of the end caps on. Put the pvc all the way around the end cap to make sure a nice seal.
3. Wrap each of your tpms sensors in poly fill to keep them from bouncing around in there. I used an old pillow for the poly fill.
4. put all your tpms sensors in and stuff more poly fill in the pipe to again prevent them bouncing around.
5. Drill out a hole on one of the end caps (i used 5/8" bit) the same size as your valve stem rubber grommet. You don't want this hole too big because it will leak. Screw the valve stem together.
6. Now put pvc cement around that end cap and put it on. Give it a couple of minutes to dry and then air that puppy up to 35lbs. Check for leaks. Boom you are done.
the following steps are optional but if you are as cool as me and like to just waste money on stupid items that no one will see you can do the following steps:
1. Get some pvc paint of your choice and spray paint that puppy.
2. Go back to the hardware store and purchase some racing decals of your choice along with a Terminator skull looking valve cap.
3. Place the dope decals on and the valve cap.
4. Add more decals for added horsepower.
5. Now take your new friend for a ride. I let him ride shotgun since he is so pimp looking, and it also lets other people know that I am not messing around with the NOS stickers all over it. Honda civic owners get really jealous when they see this.