I didn't read all 3 pages of this thread. I have made a chain like you said in your original post. But,,, make sure your snap links swivel, or that you have a swivel in both ends of the chain. Otherwise the chain gets twisted up and then it gets shorter and shorter.
And,,, don't run the chain around a tree. The chain around the tree can kill it. I also have a pre-build dog cable I bought at a hardware store. It has a plastic coating around the cable. I can put that around anything and it does not hurt whatever it is wrapped around.
I'm a little nervous tying my dog to anything that moves like the camper or the pickup. I usually tie him to the picnic table. He does get tangled under there sometimes but, I have had him for 4 years and he has learned to untangle himself fairly well. When he can't he has learned to just follow my finger around the table legs until he has more slack in the chain again.
My dog is a hyper lab too. His nickname is Stupid. :p The kids at the park love calling him stupid and not getting yelled at for it. lol. And, he loves the attention. :B