How to preserve the "sugar syrup" without using a cold storage?
Sugar is a natural preservative and provided you store it in a dark, dry, cool place it should keep for a long time. You should store it in a sterilised glass jar or bottle.

To sterilise, place the empty, open jar in a pan of cold water and bring to the boil, boiling for ten minutes. Remove, pour in the syrup, then place the lid on and return to the boiling water for another ten minutes. Dry with a clean towel and store.