I just got back from backwoods camping, each site has a wooden chest/thunderbox/toilet out in the open woods near the site. I'm not sure if the thunder is the heavy wooden lid closing or the noises that come from it. Some are out of sight of the campsite but ours was only 75ft away, fortunately the lid blocked your view if it was in use.

I could be wrong, but I don't think that is the thunder the "thunder clappers" was named after.