Looks like a glitch. On a friend's Dedi' server a few days back something must have happened following a server reboot, which caused a few tribes to have areas around their base which wouldn't allow any construction :/
Nothing to do with possible neighbouring tribes or spawn points. One moment we were able to place storage inside the build, then a reboot and suddenly couldn't place them in the same place.
Was Prim+ we were on btw so maybe an issue for that mode