A brief note
the term "resin and glass", is a very vague expression, and can refer to a whole range of products.
The most common are
POLYESTER RESIN, which IS water soluble, hence osmosis in full size boats using it.
It has to be either painted or have a gel-coat to protect it from water and sunlight, and is usually brittle.
EPOXY RESIN, is water and vapour proof, retains usually a degree of flex, but needs a top coat, to protect from the UV component in sunlight.
There are other resins, and other clothes other than glass. All have their uses.
PERSONALLY MYSELF, i only ever use epoxy resin, and seal the whole hull, inside and out, with a light weight, or finishing matt reinforcing glass or other cloth. I use the same epoxy to 'glue' the hull and superstructure, sometimes tacking things together with a flexible instant glue gel.
Works for me, and cheap insurance after spending 100's of hours on ones pride and joy