A couple of ideas,
1. Plywood Tornado hulls are easy to build and the design is in the public domain. Possibly the only design modification you would need is to relocate the main and rear bulkhead locations and the re-shape of the bean channels.
2. Since you seem to really like the Hobie 18, why not use an existing hull as a plug for a female mold. Then you could mold a set of new H 18 hulls from advanced and much lighter/stronger materials. The conventional wisdom is not to use the female mold method for a one-off project but since you allready have a male "plug" available, a lot of the work is done.

Kevin