Andy,
If you want to build a boat like that you could consider raised sections in the hulls at the critical points to support the beams. (This can be done without adding much weight if designed with care and it would be structually much better than post) 12ft surfcats are built this way. The have these raised sections and the tramp is on a 4 sided frame made of round aluminium around 50mm dia and around 3mm wall. The have around 80 sq ft of sail and no dolphin striker. The hulls are symetrical but don't need centreboards. Only drawback is this type of system needs 4 nuts to be done up to assemble the platform.

I had a look for a photo of one unfortunately only have one ofa surcat upside down when I was making some beach wheels for it. I attached it just in case it is of some use.

Regards,
Phill