I also bought a Theodor Heuss kit of EBay about five or six years ago , and didn't realise that the hull was polystyrene until I opened the box -what a shock I got!!, anyway I skinned the hull with fine glass weave cloth and coated it with laminating epoxy resin which worked ok and not too heavy , as for the printed ply parts I photo copied them and made everything from 1.5mm styrene sheet.
The daughter boat was not with the kit so I adapted the robbe Stepke daughter boat from the Berlin SAR , which is 2" too long so the dock and retriever had to a to altered to suit. I had to add weight in the stern of the model to get it lower enough for the daughter boat to be pulled back on baord.
In the end I have a fully working model that was almost scratch built .
If you look in the shows section on the main page ther are some pics of it and and my two other SAR boats plus Domonics/Bob`s Adolph bermphol on the water at Hop farm 2009
Paul.