The trap wires should be ok, just make sure they're in good shape. Replace them if necessary. I've probably had around 600lb on my 18 at once (three people) and sailed it hard - no problem. Make sure everything is in good condition. Install the front cross bar reinforcement kit if it isn't already in.

As far as mast failure, probably just don't run your diamond wires too loose (they should be tight anyway at your weight), and I wouldn't see a problem.

sm