This is quite amusing...

Jaidjen, very kindly (thanks!), put a 'hold' request in on that cabin when she spotted it was available. In the meantime I had lost patience and made the 'walk-on' reservation mentioned yesterday. I emailed the ticket centre and asked if the two could be combined and I will pay the difference. I'm still waiting to hear back but, this morning, I received the following message relating to my original reservation request:

Itinerary CONFIRMED.

Please contact us to make payment by April 14, 4:30PM Alaska time at 800-382-9229

Thank you for using Alaska Ferry Adventures!

I will try to waitlist your cabin and let you know when that happens. Sorry this took so long, but toooooo many people got involved. Any questions to me attention: LOIS
So, in the space of 24 hours, I seem to have made three reservations!! :o