Kisutch said..
What about metal stuff on board, like fin screws and leash thingy, don't those rust if you don't rinse?
Never had an issue. Even with surfboards for decades.
I know it can happen when factories are victim of unscrupulous providers and get cheap knock off parts.
You can rinse gently from time to time the gore tex vents, without touching it.
Ah, I forgot: I take care to remove any sand from the board before putting it in the bag, either with some water, towel or brush. A bit of sand in a bag will quickly ... sand ... a board.