If you still want the information, here's a quick spoiler post. You have been warned, lol. If you do use it, I hope it helps. If not, hopefully you don't do what I did and spend way too much time looking for the last one, which in my case was because I decided to explore the tunnels.
All 4 camps are on the subterranean road, note the spot where it branches off, there are 2 in each branch. If you stay on the road you'll see all of them.
Heading west, toward the bridge: Stalactite Cavern Encampment, Echoing Chasm Encampment, take the turn north right before the bridge.
South: Sunken Pit Encampment, Stony Crag Encampment.
I would also advise looking in the tents of all the camps though regardless, you may find a couple goodies.
Spoilers end.
"You know nothing of death... allow me to teach you!" Dreadlich Tamsin
Download the latest version of my Bokura no Daibouken 3 guide
here.