I have been experimenting for a while , and the best method I have found for attaching the timber to the plastic deck is ordinary styrene glue sold for plastic kits. By applying enough for one plank at a time to the deck only , it seems to melt the plastic enough to grip the wood firmly. Far better than contact adhesive , epoxy or white glue (which is useless for this) If you use the liquid variety it does not seem to stain the timber like epoxy or white glue . Coupled with using a soft (2b or more) pencil to simulate caulking it works well .Once its been varnished , (at least 3 coats) it seems watertight enough. Must admit I have not given it an endurance test.
Will try to attach a picture of my latest attempt , fore & aft decking on a RTR Riva, will be testing this when I have worked out how to deepen the colour of the simulated mahogany hull !!!!! The sharp eyed will notice the white styrene caulking.
What does everyone else use?