it ridged enough as it is.
i can't see you getting to all the small voids, it's filled with blocks of foam, without drilling a load of holes.
how are you going to seal the holes? not much sticks to whatever they are made out of.
well i was only thinking of doing the stern as there are a couple of plugs there and also i did have a crack on the top a few inches from where the engine sits but i fixed that with some of that loctite all plastics glue, so may be i will just leave it just in case.