Ideally, poly diesel fuel storage tanks need to be stored away from houses and in a bunded area.
With steel/metal tanks, your diesel fuel faces a higher risk of evaporation through radiant heat, but this isn’t an issue with poly diesel tanks. For your peace of mind, you can install your poly diesel storage tank underneath the shade for added protection.
See here for more information on base and bund requirements:
What kind of base is required for my Coerco poly diesel storage tank?