It is not a necessity that you deflate your kayak before storing it. However, it is much better to store it according to the instructions of the manufacturer. Your kayak will last much longer this way. It is always a good idea to rinse and dry your watercraft every time you use it. If you will be storing it without deflating it, you shouldn't do so with high PSI. You should also keep out of the sun and unfavorable conditions to protect its structure.