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
Seriously, IMHO you will have to be the best judge whether your fittings etc will take the weight.