As I said, most people do some variation of the Skagway to Bellingham route. In 2009, my wife and I put our truck camper on in Prince Rupert to Skagway,and had a two berth cabin. The cost of the trip was $1,064usd plus food which we would eat no matter how we traveled. Not sure that is much more than the cost of driving. Can't imagine where you came up with the cost of $13,000 more than driving. But I only get about 14 mpg with my truck camper combo and not pulling anything. LOL
Are those 9 trips one ways, or round trips, just curious? If you are headed outside to haul stuff back, it may be cheaper for you to leave your cargo trailer in Kenai and buy a new one in Oregon, to haul back north and then sell one of them, if you want to ride the ferry.