DAS modeling clay (see
http://www.doart.co.uk/acatalog/Clays.html), (scoll down) can be rolled to a very fine thickness and hold ist' shape when it dries out, the stuff i experimented upon was a grey colour but you may be able to get different colours or change the original.
I'm sure you wil find more info from a search.
There is something which dries to the consistency of soft expanded foam, i little harder than the ceiling tiles that used to be fashionable years ago, i think it is called "Model Magic". If you can find any info it may help. Because of the consistency the material is very lightweight, about a quarter of the weight of Milliput i would guess, and the finish is resiliant, rather like rubber, (i use a piece of it as a small sanding block).
I played around with this stuff some years back and never actually used it (no need on boat models) so i just hope my memory is ok.
J.