@beavercreek - I thought like you but I have to say - ruefully - that Cuprinolling the roof of a Holzmodellbau building did it no good at all; the walls were fine, but the roof, made up from wooden shingles, mounted on some sort of composite matting, buckled. It may be that it was the specific material used in the roofing. I can imagine that decking and so on is made of sterner stuff. Hence my thought about just a coat of varnish. [I intend to stand the buildings on stone slabs to prevent water rising up the walls.]