<font color=blue>I'm not sure I quite follow you. Do you mean get water out of the actual boat? Or are you noticing some sort of Osmosis with the fibre glass becoming sodden.
If it is the former then use the bilge pump to get the boat as empty as possible, bail out the remainder, finally dry out with a sponge. If it is the latter then the boat needs to come out and left standing until dried out then Osmosis treatment undertaken.
Umm, I think you mean bits of Shetland are double skinned and water has got between the skins. Thought they had bungs for access for someof it, certainly did on the old one a mate had. If not, not sure, speak to shetland thereselves, they are still in Bury St. Edmunds or close to from memory.