Alex
We don't use rails on our dogbox. Just rig them right off the top. We screwed/glued down some indoor/outdoor carpet. You can then drill a hole through the top and put a screw with the ring on it (forgive me I can't think of what they are called) my dogs are short enough I then just attach a coupler to it and then onto them. Voila they are rigging
We just run a tie strap with knots in it over the dogbox and then to the hooks in the bed of the truck. It also helps to hold the box still if it doesn't fit snug. We attach our couplers in-between the knots to keep the dogs from sliding over.
My dogs have never rigged with rails on... Just have never got around to making them. We can rig 3 dogs with no problems of anyone falling off of the box.
Here is a picture.. Not a great one.. We use to use leashes until we figured out the couplers work better for our shorter dogs. In this picture we still had the leashes.
I have also rigged them out of the back of the truck. I just tied them with a coupler to the hooks in the bed of the truck. They are too short for the dogs to jump out.. They don't get to move around as much but it works.
Don't you have a shop class in school that you can build a dogbox in?