We have been to Alaska three times, the last being 2010. Each time we crossed into Canada in upstate New York. Our 5th wheel and truck was checked from stem to stern and all was fine with everything, and we had a full fridge and freezer full. Coming back into USA we did lose some hamburg and this was due to the fact I had taken it from the wrapper and had made it up in patties. Customs told me if I had left the wrapper on that said I bought it in Alaska, it would have been fine.
I honestly think you will not have any trouble going without power for 12 hours or more. Not opening the door will keep everything just fine. Having said that, I wouldn't leave the ferry and then boondock. :)
Have a wonderful trip and hopefully you will post your travels on RV Net or a blog so we can follow along with you.
