There's lots of ways to say no.The wife’s brother bought a boat without a place to park it. He originally asked my wife if he could store it in our pole barn. She told him we didn’t have the room.
Now he wants to park it here, but (I’m assuming) outside. Minus all the inconveniences that entails and us really not having the room....
Simply tell him "sorry, no. We still don't have the room that hasn't changed since you asked yesterday"
Then give him the list of boat storage places you looked up.
Then if he asks again tell him your insurance company advised you not to do it.
Then if he asks again and is the kind of guy that won't accept that he can't always get what he wants for free, sigh and tell him you guess you can do it, and quote him a price double what the storage places want and require a year in advance. "It's for insurance; and here, sign this paper that says we have zero liability. My notary is waiting."
That should solve it.