When only one storage location is used, you can make the required settings to default storage location in the delivery. Use Tcode OVL3 to make the settings and the storage location will be determined automatically in the delivery.
TO default storage location in the order we have to use a userexit. Since you are using only one storage location, it doesn't make any difference even if storage location is not determined in the order. It is not advisable because, using Userexits will decrease the system performance.