I've got three kayaks and a large roof box all on pulleys in the roof of the garage. None are as heavy as your RIB; as Spartacus says make sure that you fit to rafters or concrete. I guess none of us here would want to say go for it and it will be fine, as you might sue us if it failed
![wink](https://www.rib.net/forum/images/smilies/wink.gif)
Seriously, IMHO you will have to be the best judge whether your fittings etc will take the weight.