I would have to say, waterproof has got to be the way to go on a RIB.
Even if its not one of ours.
I would never recomend a Slashproof/Water resistant unit on a rib.
You could have spent a bit more and got a waterproof unit.
Then if it let in water you would have some come back.
There are some good water proof radio's on the market these days for not a lot more money.
Sorry to kick you when your down.
Still worth speaking to Silva, never know someone there may be feeling kind up there!