When the boat is stored exposed to the sun outside water for a longer while, it should be covered up or moved to a place in the shade.
Best reduce air pressure to min. 0.2 bar.
Direct exposure to sunlight over a longer period is detrimental to the boat material – Rubber dries out and becomes porous. To prevent that, do not leave the boat unnecessarily exposed to direct sun. Apart from that regularly treatment of the boat by applying boat care agent to prevent the boat-skin to dry out, will keep it supple.