Mona is a magical place!
I know you need a permit to camp on the island, but not sure about overnight in a boat. I guess you could begin with the contact number for camping (787) 722-1726. I know they limit the # of folks on island, and it is totally off limits during turtle nesting times.
I was lucky enough to go out there in the 70s on a Coast Guard helo several times. Absolutely amazing place. Enjoy and please post pictures when you return.