Hey Nik
I asked this Q a while back and the answer seemed to be that because no light really gets into the flooded compartment, no scum will grow!
I'm blocking mine up this year just to see how different the boat reacts on acceraration and slow speeds.
Safeboatskin is what im going to apply to the hull and tubes, you can always stick a rag on a stick and have a go at applying this stuff to the inside of the hull........
Bri