What bothers you about using a carriage bolt & wing nut?

I'm not at all familiar with how this fits into a PM, but if you're looking at ease-of-use rather than an aesthetic consideration for the wing nut you could use a stainless steel T-nut embedded then covered on one side with a piece of fitted plywood. Opposite side would take a stainless threaded rod of suitable length with a plastic knob (best w/brass threaded insert inside) or perhaps an antique doorknob securely fixed to one end.

Or make up a custom knob from plywood scraps with another T-nut embedded in one side.

Carriage bolts have a functional elegance but a little creativity can be brought to bear on implementing an alternative.

I am thinking of embedding something like this in the wood and make a divit for the bolt head and more epoxy  and coat with epoxy the wwasher  on rudder and take apart portion.

http://www.homedepot.com/p/Crown-Bolt-5-16-in-Torque-Washer-2-per-Bag-47628/203577221

If you come up with a better idea let me know.

I think they sell these at Ace hardware too