first give the faces around your base the same material id as the ground texture, and have you deleted the unwanted faces from underneath the base where you dont walk on and detached it from your skybox?
1: no
2: no, detach the base from the skybox by highlighting all of the bases faces and clicking deatch and call it base 01
3: give the blue area around your base a id of 2 (should be same as your ground texture)