Gareth,
I did consider two rigs.
If used in a sailing school it would be very handy and not very expensive addition. Just an extension that plugs into the mast and a different sail.
I agree, that to get the cost of the boat cheap enough for the family budget rottomoulding could be an option.
I don't suppose it is something that you'd consider before
confirming the existence of a good market.

Do you have any idea of the tooling costs?

Also I'd really like to be able to do some weight calculations on RM hulls.
In foam sandwich the hulls would be around 11 to 12 kg each max and could be as low as 10kg because they are so simple. I'd love to know the weight of an equivalent rottomould hull.

The hulls will not have the normal high loadings from bridle etc because the free standing rig will transfer the loading through the front beam. They just need reasonable tortional strength between the beams although sheeting from the ends of the rear beam instead of the centre will help a little with this.
While RM may be needed it would be a shame because it just isn't a nice as foam sandwich.

Regards,
Phill