Wouter,

3kg added to something that is only 11-12kg is a pretty big step. For the expense and labor not to mention time in design and testing other than the self satisfaction of "doing it yourself" it does not seem very practical.

Polystyrene foam does not have very good compression resistance, so it will be very difficult to get the compression needed to properly consolidate a laminate that I would trust for a mast. The idea has some merrit though as we have used it for one off "lost mold" projects in the past. Poor acetone in the tube when you are done and it will disolve the foam and you have a hollow tube left over. There are some other methods that work even better, but they require yet another level of equipment.

Matt